SAT Physics Subject Test - Practice Test 3

SAT Physics Subject Test - Practice Test 3
Do not use a calculator. To simplify numerical calculations, use g= 10 m/s2.

PART A

Directions: In this section of the exam, the same lettered choices are used to answer several questions. Each group of questions is preceded by five lettered choices. When answering questions in each group, select the best answer from the available choices and fill in the corresponding bubble on the answer sheet. Each possible answer may be used once, more than once, or not at all.
Questions 1-3:
(A) Position
(B)  Displacement
(C) Speed
(D) Velocity
(E) Acceleration

1.The slope of a position-time graph.

 
2. The slope of a velocity-time graph.

3. The area bounded by the function, the x-axis, and the time interval in a velocity-time graph.

Questions 4-6:
(A) Electric field
(B) Electric force
(C) Electric potential
(D) Electric potential energy
(E) Capacitance

4. A scalar quantity that reflects the ability or tendency of a charge or group of charges to generate electric energy on another charge that occupies a particular point in space.

5. The means of quantifying the amount of charge stored on two equally and oppositely charged objects.

6. A vector quantity representing the alteration of space surrounding point charges and charged objects, which is associated with electric force.

Questions 7-9:

7. Which lens/mirror is a divergent optical instrument?

8. Which lens/mirror will produce a real image on the far side of the optical instrument?

9. Which lens/mirror will produce a large upright image on the near side of the optical instrument?

Questions 10-12:

Which of the products of nuclear reactions listed above is released during the following nuclear reactions?

10. Alpha decay

11. Beta decay

12. Fission

PART B

Directions: This section of the exam consists of questions or incomplete statements followed by five possible answers or completions. Select the best answer or comple­tion, and fill in the corresponding bubble on the answer sheet.

Questions 13:
What is the maximum height reached by a ball thrown upward at 30 meters per second?
(A) 1.5 m
(B) 3.0 m
(C) 30 m
(D) 45 m
(E) 90 m

Questions 14:
A mass initially at rest undergoes a uniform acceleration a during a time interval t. The mass reaches a speed v when it has been displaced a distance x.The mass continues moving with acceleration a.What are the speed and displacement of the mass when the time has doubled, 2 r?


Questions 15:
Which is NOT true regarding acceleration?
(A) Some accelerating objects have constant speed.
(B) Acceleration is the rate of change in velocity.
(C) Acceleration is the slope of a position-time graph.
(D) Acceleration can be positive, negative, or zero.
(E) Acceleration can involve a change in either speed or direction.


Questions 16:
The pilot of an airplane needs to travel directly north. However, a strong crosswind is blowing out of the west, as shown above. Which diagram below indicates the direction in which the pilot must steer the plane to compensate for the crosswind so that the plane moves north?


Questions 17:
A ball is thrown horizontally with a speed v drops a distance y and moves horizontally a distance If the ball is thrown with the same horizontal speed v from a height of 2y, what is its new horizontal displacement?
(A) x
(B) √2x
(C) 2x
(D) 4x
(E) 16x


Questions 18:
A projectile is launched with an initial velocity v at an upward angle θ, as shown above. During the entire motion, which variable(s) remain(s) constant?
I. Horizontal component of velocity
II. Vertical component of velocity
III. Acceleration
(A) I only
(B) II only
(C) III only
(D) I and II only
(E) I and III only

Questions 19-20:
The diagram below depicts a mass, m, being pulled along a rough horizontal surface by a force F acting at an angle θ above the horizontal. The force of friction acting on the block is f, and the coefficient of friction is μ.

19. Which of the following describes the frictional force, f, if the resulting motion is constant velocity?
(A) 0
(B) μmg
(C) μmg cos θ
(D) F cos θ
(E) F sin θ

20. Which of the following is true regarding the normal force?
(A) N = mg
(B) N= mg cos θ
(C) N= mg sin θ
(D) N= mg - Fcos θ
(E) N= mg - Fsin θ


Questions 21:
Two masses, m₁ = 3.0 kilograms and m₂ =5.0 kilograms, are connected by a string, which is draped over a pulley. The masses are released from rest. Determine the magnitude of the acceleration of mass m₁
(A) 2.5 m/s²
(B) 3.0 m/s²
(C) 4.0 m/s²
(D) 4.5 m/s²
(E) 5.0 m/s²

Questions 22:
A rocket moves upward during its launch. Which of these is true?
(A) Exhaust gases push on Earth, creating an equal and opposite upward force.
(B) Exhaust gases push on air molecules, creating an equal and opposite upward force.
(C) Exhaust gases pushed backward by the rocket are the action force. They create an opposite and equal reaction force that moves the rocket opposite the motion of the gas.
(D) The force of the exhaust gases must be small so that they don’t add too much downward force to gravity. If they do, the rocket will not have enough upward force.
(E) All of these are incorrect.

Questions 23:
When an object is thrown upward in the absence of air resistance and reaches the top of its trajectory, it has an instantaneous velocity of zero. At this point, the net force acting on the object is
(A) 0
(B) equal to the weight of the object
(C) equal to the mass of the object
(D) g
(E) changing direction

Questions 24:
A 10-kilogram mass is suspended by two ropes, as shown above. Rope 1 is attached to a vertical wall. Rope 2 is attached to the horizontal ceiling at an angle θ = 53° as measured from the ceiling. The tensions in the ropes are T₁ and T₂, and the weight of the object is w. Which of the following is NOT true?
(A) T₂ >T₁
(B) w >T₁
(C) w >T₂
(D) T₂ cos θ = T₁
(E) w = T₂ sin θ


Questions 25:
Two masses, connected by a string, tire pulled along a frictionless surface by a 6-newton force, as shown above. Determine the tension in the string between the masses.
(A) 1N
(B) 2 N
(C) 3 N
(D) 4N
(E) 5 N

Questions 26:
An object moving in a circular path completes one circumference. Which statement(s) below is (are) true?
I. The displacement is zero at the conclusion of its motion.
II. The average speed is zero at the conclusion of its motion.
III. Velocity changes during its motion.
IV. The acceleration is zero during its motion.
(A) I only
(B) I and II only
(C) I and III only
(D) IV only
(E) II and IV only

Questions 27:
A mass is pulled up a rough incline at constant speed, as shown above. The coefficient of kinetic friction is pi. Which diagram is correct?



Questions 28:
A mass is moving in a circle as shown above. The motion is uniform, having constant speed. Which set of vectors correctly depicts the velocity and acceleration at point P, shown in the diagram?


Questions 29:
Mass m is positioned 1.0 meter from the center of a circular disk that is rotating with increasing speed, as shown above. The coefficient of friction between the mass and the disk is 0.40. What maximum speed can the mass obtain before it slips off the rotating disk?
(A) 1.0 m/s
(B) 1.4 m/s
(C) 2.0 m/s
(D) 2.8 m/s
(E) 4.0 m/s

Questions 30-31:
A roller coaster car passes through a frictionless vertical circular loop in the track, as shown in the diagram below. When the roller coaster car is at the very top of the loop, its instantaneous velocity is directed in the -x-direction.


30. Which force diagram is correct at the instant that the roller coaster car is at the top of the loop?


31. The loop has a radius of 10 meters and the velocity at the top of the loop is 10 meters, per second. What is the apparent weight of a 50-kilogram passenger riding in the roller coaster car?
(A) 0 N
(B) 25 N
(C) 50 N
(D) 100 N
(E) 500 N

Questions 32-33:
A 25-newton force is applied to a 5.0-kilogram mass initially at rest on a frictionless surface.

32. Determine the work done on the mass to move it 10 meters.
(A) 2.5 J
(B) 50 J
(C) 125 J
(D) 250 J
(E) 1,250 J

33. Determine the speed of the mass when it has been displaced 10 meters.
(A) 2 m/s
(B) 4 m/s
(C) 5 m/s
(D) 10 m/s
(E) 20 m/s

Questions 34-35:
A 3.0-kilogram mass tied to a string is initially at rest at point P, as shown in the diagram below. The mass is released and oscillates as a pendulum. Point Q is the lowest point reached by the mass suspended from the string.


34. What is the work of gravity done on the mass as it moves from point P to point Q?
(A) 2 J
(B) 3 J
(C) 4 J
(D) 5J
(E) 6 J

35. What is the maximum speed reached by the mass during the oscillation?
(A) 2 m/s
(B) 3 m/s
(C) 5 m/s
(D) 6 m/s
(E) 9 m/s
_____________________________________________________________

Questions 36:
An object is lifted at constant velocity by a force F to a height h. To accomplish this in time t, power P is required. In order to lift the object to the same height h in half the time, ½ t, what force and what power are needed?
(A) ½ F and ½ P
(B) ½ F and P
(C) F and 2P
(D) 2F and P
(E) 2F and 2F


Questions 37:
Two identical 2.0-kilogram masses are moving in the +x-direction as shown in the diagram above. The left mass has a speed of 3.0 meters per second, and the right mass has a speed of 1.0 meter per second. When the masses collide, they stick to one another. What is the final speed of the combined masses after the collision?
(A) 1.0 m/s
(B) 1.5 m/s
(C) 2.0 m/s
(D) 4.0 m/s
(E) 8.0 m/s

Questions 38:
The magnitude of impulse is equal to:
I. FΔd
II. FΔt
III. mv
IV. mΔv
(A) I only
(B) II only
(C) II and III only
(D) II and IV only
(E) II, III, and IV only

Questions 39:
An astronaut weighs 600 N on Earth. What is the astronaut’s mass on the Moon,where the acceleration of gravity is
1/6  that of Earth?
(A) 0 kg .
(B) 10 kg
(C) 60 kg
(D) 100 kg
(E) 600 kg

Questions 40:
Several planets orbit a large central star that has a mass The mass of each planet is given in terms of m, and their orbital radii are given in terms of r. Which planet experiences the greatest gravitational force pulling it toward the central star?


Questions 41-42:
A large sphere located at the origin contains a +20-coulomb charge. A small sphere located 4 meters to the right of the large sphere has a charge of -1 coulomb.


41. The force that the -1-coulomb charge pulls on the +20-coulomb charge is


42. The force acting on the -1-coulomb charge at its present position is F_E. What will the force acting on the -1-coulomb charge become if the -1-coulomb charge is moved to Point P?

_____________________________________________________________


Questions 43:
Two charges and point P form an equilateral triangle as shown above. One charge is negative, and the other is positive. However, the magnitude of the charges is the same.What is the direction of the electric field at point P?
(A)  +x
(B)  -x
(C)  +y
(D)  -y
(E)  The field of each charge cancels, and no field exists at point P.

Questions 44:
Two positively charged spheres are released and begin to move. Which statement regarding the force, acceleration, and velocity of these charges is true?
(A) Force increases, acceleration increases, and velocity decreases.
(B) Force increases, acceleration increases, and velocity increases.
(C) Force decreases, acceleration decreases, and velocity decreases.
(D) Force decreases, acceleration decreases, and velocity increases,
(E) Force decreases, acceleration increases, and velocity decreases.

Questions 45:
A proton and an electron are placed between two plates of equal and opposite charge. Assume the attraction of each particle to the other is insignificant compared with their attraction to the plates. Which of these is true?
(A) The proton and electron move in the same direction, and the proton has a higher acceleration.
(B) The proton and electron move in the same direction, and the electron has a higher acceleration.
(C) The proton and electron move in opposite directions, and the proton has a higher acceleration.
(D) The proton and electron move in opposite directions, and the electron has a higher acceleration.
(E) The proton and electron move in opposite directions and have the same accelerations.


Questions 46:
What is the velocity of a 1.0-kilogram sphere with a -3.0-coulomb charge that is accelerated from rest through a 6.0 V potential difference, as shown above?
(A) 2.0 m/s
(B) 3.0 m/s
(C) 6.0 m/s
(D) 12 m/s
(E) 18 m/s

Questions 47:
How is the capacitance of a capacitor affected when the area of the plates is doubled and the distance between the plates is also doubled?
(A) ¼ its original value
(B) ½ its original value
(C) remains the same
(D) 2 times greater
(E) 4 times greater

Questions 48-50:
The following diagram depicts a 120-volt household circuit containing three electrical components with resistances R₁= 120 ohms, R₂ = 240 ohms, and R₃ = 240 ohms. Switches X, Y, and Z are all originally in the open position.


48. What current is following through point P when switches X and Y are closed?
(A) 1.0 A
(B) 1.5 A
(C) 2.0 A
(D) 3.0 A
(E) 6.0 A

49. What current is flowing through R₁ when switches X and Y are closed?
(A) 1.0 A
(B) 1.5 A
(C) 2.0 A
(D) 3.0 A
(E) 6.0 A

50. Switch Z is closed. How much power is dissipated in R₃?
(A) 15 W
(B) 20 W
(C) 30 W
(D) 40 W
(E) 60 W

Questions 51:
Which answer is consistent with a replacement lightbulb that will increase the intensity(brightness) of the light in a room?
(A) Use a lightbulb with less resistance, which restricts the current flow and results in a lower rate of energy dissipation.
(B) Use a lightbulb with less resistance, which allows more current to flow and results in a higher rate of energy dissipation.
(C) Use a lightbulb with less resistance, which allows more current to flow and results in a lower rate of energy dissipation.
(D) Use a lightbulb with more resistance, which restricts the current flow and results in a lower rate of energy dissipation.
(E) Use a lightbulb with more resistance, which allows more current to flow and results in a higher rate of energy dissipation.

Questions 52-54:
A horseshoe magnet is positioned as shown in the diagram below.

52. What is the direction of magnetic force acting on an electron if it is moving in the -x-direction at the instant that it is located at point P?
(A) The magnetic force is 0 and has no direction.
(B) +y
(C) -y
(D) +z
(E) -z

53. What is the direction of magnetic force acting on a proton if it is moving in the +y-direction at the instant that it is located at point P?
(A) The magnetic force is 0 and has no direction.
(B) +y
(C) -y
(D) +z
(E) -z

54. What is the direction of magnetic force acting on a wire passing through point P that is carrying a current into the page in the -z-direction?
(A) The magnetic force is 0 and has no direction.
(B) +x
(C) -x
(D) +y
(E) -y


Questions 55:
A magnet is moved into a coil of wire that contains a resistor with resistance The magnet enters the coil at constant velocity. Which statement is NOT correct?
(A) As the magnet enters the coil, an emf, £, is induced in the wire.
(B) As the magnet enters the coil a current, SIR is induced in the wire.
(C) Doubling the speed of the magnet doubles the induced current.
(D) Reversing the direction of the magnet has no effect on either the magnitude or the direction of current as long as the speed remains the same.
(E) Doubling the magnetic field doubles the induced emf.

Questions 56-58:
The diagram below shows mass m suspended from a spring. The mass is oscillating between positions I and III. These positions represent the amplitudes, maximum displacements above and below the equilibrium position, experienced during the oscillation. Position II is the equilibrium position and lies midway between positions I and III.


56. At which position(s) is the useful potential energy of the oscillation system zero?
(A) I only
(B) II only
(C) III only
(D) I and II only
(E) I and III only

57. At which position(s) is the net force on the mass the greatest?
(A) I only
(B) II only
(C) III only
(D) I and II
(E) I and III

58. What is the effect on the period, T, of the oscillation if mass m is replaced with mass 2 m?
(A) ¼ _T
(B) ½ T
(C) √2/2 T
(D) √2
(E) 4 T
______________________________________________________________

Questions 59:
In a standing wave, a node is the position where
(A) constructive interference occurs
(B) destructive interference occurs
(C) amplitude is maximum
(D) Both A and C
(E) Both B and C

Questions 60:
Which of the following must occur in order to increase the intensity of light?
(A) Increase the wavelength
(B) Increase the frequency
(C) Increase the amplitude
(D) Decrease the wavelength
(E) Decrease the frequency

Questions 61:
Two wave forms interfere with each other in a manner that creates a beat frequency. One wave has a frequency of 12 Hz, and the other has a frequency of 8.0 Hz. Determine the beat frequency.
(A) 0.67 Hz
(B) 1.5 Hz
(C) 4.0 Hz
(D) 10 Hz
(E) 20 Hz


Questions 62:
In the diagram above, a ray of light refracts as it travels through three mediums: 1, 2, and 3. Rank the indexes of refraction from greatest to least.
(A) n₁ > n₂ > n₃
(B) n₂ > n₁ > n₃
(C) n₃ > n₁ > n₂
(D) n₁ > n₃ > n₂
(E) n₂ > n₃ > n₁

Questions 63-64:
Light with wavelength A is incident on two narrow slits spaced d meters apart. A distinct pattern of alternating bright and dark regions is visible on a screen located L meters behind the slits. The second bright region (maximum) is observed to be x meters from the central bright maximum. The paths of the rays of light, extending from each slit to the second bright maximum, are shown converging at the second maximum.


63. The i path difference
(A) 2λ
(B) 2xλ
(C) xλ/L
(D) 2x/L
(E) 2x

64. Which of the following is true regarding the above experiment?
(A) The experiment provides evidence that light has a wave characteristic.
(B) Light passing through each slit diffracts into circular wave fronts.
(C) The light from each slit interferes to create the resulting bright maximums and dark minimums seen on the screen.
(D) The experiment must be conducted with monochromatic light.
(E) All of these are true.

Questions 65-66:
The specific heat capacity of liquid water is approximately 4,000 joules per kilogram • kelvin. The heat of fusion of water is approximately 3 × 10⁵ joules per kilogram, and the heat of vaporization of water is approximately 23 × 10⁵ joules per kilogram. Consult the heating-cooling curve below to answer the following questions



65. How much heat energy is needed to melt 0.20 kilograms of ice initially at 0°C and then raise its temperature to 50°C?
(A) 2,000 J
(B) 4,000 J
(C) 40,000 J
(D) 60,000J
(E) 100,000 J

66. How much heat energy is needed to convert 10 grams of liquid water at 100°C into its gaseous state?
(A) 40J
(B) 3,000 J
(C) 23,000 J
(D) 40,000 J
(E) 2,300,000J
________________________________________________________

Questions 67:
Which statement is NOT true when two systems with different temperatures come into contact with each other?
(A) Probability will drive the system toward a random equilibrium state.
(B) The natural direction of heat flow will be from the system with the higher temperature to the system with the lower temperature.
(C) Heat flow continues until thermal equilibrium is reached.
(D) Once thermal equilibrium is reached, no net heat flow occurs
(E) Entropy is reduced in the process.

Questions 68:
Two metal blocks are identical in every respect except for their thickness. Block 2 is twice as thick as block 1. A heat source is applied equally to both blocks. During time t, heat Q is transferred through block 1. During the same amount of time, how much heat is transferred through block 2?
(A) ¼ Q
(B) ½ Q
(C) 1 Q
(D) 2 Q
(E) 4 Q

Questions 69:
During a thermodynamic process, 2,400 joules of heat are removed from a gas while 600 joules of work are done by the gas. What is the change in internal energy of the gas?
(A) -3,000 J
(B) -1,800 J
(C) 0 J
(D) +1,800 J
(E) +3,000 J

Questions 70-71:
In the photoelectric effect experiment, photons of light are shined on a metal, resulting in the ejection of electrons that then flow as a current through a circuit. The amount of current can be measured with an ammeter placed in series in the circuit. An adjustable battery is reversed in the circuit. It can be adjusted so that the current is canceled. When the flow of current is stopped, the voltage of the battery is equal to the voltage of the photocell. It may be assumed that the threshold frequency has been reached.

70. What is the effect of increasing the intensity of the light shined on the photocell?
(A) The current flowing in the circuit is increased.
(B) The threshold frequency is increased.
(C) The kinetic energy of the emitted electrons is increased.
(D) The voltage of the photocell is increased.
(E) Both C and D

71. What is the effect of increasing the frequency of the light shined on the photocell?
(A) The current flowing in the circuit is increased.
(B) The threshold frequency is increased.
(C) The kinetic energy of the emitted electrons is increased.
(D) The voltage of the photocell is increased.
(E) Both C and D
______________________________________________________


Questions 72:
The nuclear reaction shown above is an example of
(A) Alpha decay
(B) Beta decay
(C) Gamma decay
(D) Fission
(E) Fusion

Questions 73:
Which word best describes uranium-238 and uranium-235?
(A) Molecules
(B) Ions
(C) Isotopes
(D) Nucleons
(E) Nuclides

Questions 74:
Which statement regarding the forces in the nucleus is NOT correct?
(A) The strong force attracts protons to protons.
(B) The strong force attracts neutrons to both protons and other neutrons.
(C) At short distances, the strong force is stronger than the electric force.
(D) Adding neutrons to a nucleus adds to both the strong force and the electrostatic force.
(E) When the ratio of neutrons to protons falls outside of an optimal range, the nucleus becomes unstable.

Questions 75:
Which of the following is an electrical component that can amplify a signal and act as a switch?
(A) Capacitor
(B) Power supply
(C) Resistor
(D) Superconductor
(E) Transistor

ANSWER KEY
Practice Test 3


DIAGNOSTIC CHART

SCORING YOUR TEST
How to Determine Your Raw Score
Your raw score is the amount of correctly answered questions minus the incorrectly answered questions multiplied by ¼. An incorrecdy answered question is one that you bubbled in, but was incorrect. If you leave the answer blank, it does not count as an incorrect answer.


ANSWERS EXPLAINED

Answer 1:
(D) Slope is the rise, Ay, divided by the run, Ax. The rise of a position-time graph is position, in meters. The run is time in seconds. The slope has the units of meters per second. Slope can be positive or negative, indicating direction. Speed is not correct because it is the absolute value of velocity and consists of magnitude without a specific direction.

Answer 2:
(E) The rise of a velocity-time graph is velocity in meters per second. The run is time in seconds. The units of slope, meters per second per second, match the units of acceleration.

Answer 3:
(B) The area bounded by a function can be determined by multiplying the rise by the run. The product of the rise, in meters per second, and the run, in seconds, is meters. This is the unit of displacement.

Answer 4:
(C) Also known as voltage, electric potential is the potential ability to generate electric energy should a charged particle occupy a particular point in space. The charged objects surrounding the point in space generate this potential. When a new charged object is positioned at the point in space, it acquires potential energy due to the surrounding charges.

Answer 5:
(E) Capacitance is the amount of charge, Q, stored per voltage, V, measured in units of farads.

Answer 6:
(A) Charges are surrounded by an electric field. This is similar to the electric potential in question 4. The electric field is the capability of the charge to create an electric force on any other charge that occupies a particular location within the electric field.

Answer 7:
(C) The concave lens is a diverging lens.

Answer 8:
(A) A converging lens will form a real and inverted image on the far side of the lens from the object if the object is placed outside of the focal length.

Answer 9:
(B) A converging lens will form a virtual and upright image on the near side of the lens if the object is placed inside of the focal length. This is the effect produced by a magnifying lens.

Answer 10:
(E) An alpha particle is the nucleus of a helium atom. It has a charge of +2.

Answer 11:
(A) A beta particle is an electron ejected from a neutron. As a result, the neutron becomes a positive proton. Beta particles have a charge of -1.

Answer 12:
Neutrons are generally released as a by-product of fission. Neutrons have a neutral charge.

Answer 13:
(D) At the top of its flight, the ball will have an instantaneous velocity equal to zero. As a result, the initial and final velocities are both known. The vertical displacement is needed.


Answer 14:
(D)

Answer 15:
(C) Acceleration is the slope of a velocity-time graph. It is not the slope of a posi­tion-time graph. Choice A is good distracter. However, this scenario can be true for objects that are changing direction at constant speed, such as objects in uniform circular motion.

Answer 16:
(B) To travel north, the plane must have a component of velocity directed north. To overcome the eastward wind, the plane must also have a component of velocity that opposes the wind and is therefore directed to the west. Resolving the components results in a true velocity directed northwest.

Answer 17:
(B)

Answer 18:
(E) Acceleration due to gravity acts on only the motion in the vertical direction. The acceleration remains a constant 10 meters per second squared downward. This action continually changes the vertical component of velocity. Horizontal velocity is unaffected by acceleration due to gravity and continues unabated in the horizontal direction.

Answer 19:
(D) At first glance, answer B may appear to be the obvious choice. However, the normal force is not always equal to an object’s weight. The y-component of force F must be included.
N = mg-F sinθ
f =  μ(mg - F sin θ)
This is not one of the available answers. The key to this problem is the motion experienced by the object. In order for the velocity to be constant, the fric­tional force must be opposite in direction but equal in magnitude to the com­ponent of force acting in the direction of motion.
f = F_x = F cos θ

Answer 20:
(E) The component of force F pulling in the vertical direction can be described as Fsin 0. The normal force, N, is reduced by the amount of force pulling in the vertical direction.

Answer 21:
(A) The masses are connected by a string and therefore act as if they were a single system with a mass of 8.0 kg. Mass m_l is being pulled in one direction by the force of gravity. Mass m₂ is being pulled in the other direction by the force of gravity.

Answer 22:
(C) Rockets work in the vacuum of space as well as on Earth. Therefore, their motion cannot be the result of pushing against either Earth or air molecules. The expulsion of gas is the action force, and the reaction force is the motion of the rocket in the opposite direction.

Answer 23:
(B) The force acting on the object remains mg, its weight, throughout its flight. As the object rises, the force acts to slow it down. Upon reaching its highest point, the force acts to change the object’s direction and bring it back to the ground. However, the force acting on the object never changes.

Answer 24:
(C)

In order for the mass to remain stationary, the vertical component of T₂ (T₂ sin θ) must be equal to w. Since T₂ is the hypotenuse of a right triangle,it is greater than T₂ sin θ. Therefore, T₂ must be greater than w.

Answer 25:
(B) Determine the acceleration of the entire system.

Answer 26:
(C) Since the object returns to its original position, displacement is zero. Direction is continuously changing, and this means that velocity is changing. Therefore, answers I and III are true. Speed is a measure of distance divided by time. Even though displacement is zero, the distance traveled is not zero. This eliminates answer II. Acceleration changes direction during the motion but is never zero, eliminating answer IV.

Answer 27:
(E) Four forces are present: the force of gravity acting downward, the normal force acting perpendicular to the incline, tension pulling the object up the incline, and friction acting to oppose the motion.

Answer 28:
(B) Velocity is tangent to the path in the direction of motion. Centripetal accelera­tion is always directed toward the center of rotation and is perpendicular to the velocity.

Answer 29:
(C) The friction force creates the centripetal force needed to keep the object moving in a circle.


Answer 30:
(E) Only two forces are acting on the car as it is in the loop: the force of gravity, F_g, and the normal force, N. The force of gravity always acts downward. The normal force always acts perpendicularly to the plane of the surface upon which the mass rests. In this case, that would be downward. The velocity is directed in the -x-direction, but that is not a force. Instead, it is the result of the inertia of the car.

Answer 31:
(A) Apparent weight is a measure of the normal force acting on a mass. The centripetal force, F_c, is the sum of the two forces acting on the passenger in the car. Setting F_c equal to the sum of F_g and N yields:

In this case, the passengers would feel weightless at the instant the roller coaster reaches the top of the loop.

Answer 32:
(D)


Answer 33:
(D) The work-kinetic energy theorem states that work is equal to a change in kinetic energy. Use the work found in the previous answer.


Answer 34:
(E) The work done by gravity is equal to the change in gravitational potential energy, A U, as the object moves through the vertical distance of 0.2 m above point Q.


Answer 35:
(A) This can be solved using conservation of energy. The 6 joules of gravitational potential energy at point P become kinetic energy, K, at point Q.


Answer 36:
(C) Both times, the object is lifted to the same height h at constant velocity. To overcome gravity and move the object at constant speed, the upward force must be equal to the force of gravity. Therefore, each time the needed force is the same regardless of the time during which the force acts. Moving the object the same vertical distance h requires the same amount of work against the force of gravity. However, in order to do this in half the amount of time, twice the power is needed.


Answer 37:
(C) Momentum is conserved before and after the collision.


Answer 38:
(D) Impulse, J, is equal to the force multiplied by the change in time. It is also equal to the mass multiplied by the change in velocity, which is known as the change in momentum. It is not equal to the momentum itself but, rather, the change in momentum.

Answer 39:
(C) Mass is not affected by changes in the acceleration of gravity. Even though the problem asks for the mass on the Moon, the weight on Earth can be used to determine the mass on Earth. This value is equal to the mass on the Moon.
w= mg
600 N = m(10 m/s²)
m = 60 kg

Answer 40:
(B) Try each possibility in Newton’s law of gravitation.

Choice B results in the largest possible gravity.

Answer 41:
(E) According to Newton’s third law, the two charges pull on each other with the same force.

Answer 42:
(E)

Coulomb’s law is very similar to Newton’s law of universal gravitation. When the -1 C charge is at point P, the radial distance will be 1/2 of what it was originally. The result is consistent with the inverse square law.


Answer 43:
(B) Identify the charges as charge 1, q₁ and charge 2, q₂. The electric field points toward the negative charge, so the electric field of charge 1, E₁ points toward charge 1. The electric field points away from the positive charge, so the elec­tric field of charge 2, E₂, points away from charge 2. These two vectors can be added using vector addition to find the total electric field due to both charges.

The resulting electric field points in the -x direction.

Answer 44:
(D) Since the spheres are positively charged, they will repel one another. As they begin to move farther away from one another, the force acting on them will decrease according to Coulomb’s law. A reduction in force leads to a reduc­tion in acceleration. Velocity, however, will continue to increase because even though acceleration is decreasing, it continues to act in the direction of motion and continues to increase the speed of the charged spheres.

Answer 45:
(D) Protons and electrons have the same magnitude of charge, e, but opposite signs. As a result, the charged electric plates apply an equal electric force on the similarly charged proton and electron, but in opposite directions. The acceleration of each particle is dependent upon its mass. Electrons have a much smaller mass than protons. As a result, the same force applied to an electron will cause the electron to have a greater acceleration than the more massive proton.

Answer 46:
(C) This problem can be solved using conservation of energy. The electric poten­tial energy is converted into kinetic energy.


Answer 47:
(C) Capacitance is proportional to the area of the plates divided by the distance between them. Doubling both area and distance will result in the capacitance remaining the same.

Answer 48:
(B) The resistors can be added in parallel to determine their total resistance.


Answer 49:
(A) Resistor 1 is wired in parallel, and the voltage drop across it will be equal to the voltage of the battery. Use Ohm’s law, V = IR, to solve for the current flowing through R₁



Answer 50:
(E) Power can be determined two ways. The current flowing through R₃ can be found in the same manner as in the previous problem.


Answer 51:
(B) A bulb with less resistance will allow more current to flow. In households, the voltage is constant. So increasing the current will increase the power accord­ing to P = IV. Power is the rate of energy dissipation. Increasing the power increases a bulb’s brightness.

Answer 52:
(E) The right-hand rule states that the thumb of the right hand points in the direction of motion of a charged particle (the -x-direction in this case), the extended fingers point in the direction of the magnetic field (down the page in this case), and the palm of the hand points in the direction of the force (out of the page in this case). However, the particle is an electron. Electrons experi­ence the complete opposite force. So the direction of force is into the page, -z-direction. As an alternative, you can use the left hand to determine the direction of magnetic force on negative charges.

Answer 53:
(A) In this case, the charged proton is moving parallel to the magnetic field. No magnetic force acts on the proton if it is moving completely parallel to the field.

Answer 54:
(C) The right-hand rule states that the thumb of the right hand points in the direc­tion of either the motion of a charged particle or the current in a wire (the -z-direction in this case), the extended fingers point in the direction of the magnetic field (down the page in this case), and the palm of the hand points in the direction of the force (to the left of the page in this case, the -x-direction).

Answer 55:
(D) Reversing the magnet would reverse the direction of the current.

Answer 56:
(B) At position II, the total energy is in the form of kinetic energy, K, and potential energy is zero.

Answer 57:
(E) At position I, the constant force of gravity is greater than the variable force of the spring. At position III, the variable force of the spring is greater than the constant force of gravity. At position II, the constant force of gravity is equal to but in the opposite direction of the variable force of the spring. Therefore, there is no net force at position II.

Answer 58:
(D) The period of a spring depends on the mass and the spring constant.


Answer 59:
(D) At the nodes, waves add destructively and there is zero amplitude.

Answer 60:
(C) Light intensity is directly proportional to the amplitude of a wave. Frequency and wavelength have no effect on the intensity of light.

Answer 61:
(C) Beat frequency is the difference between two interfering waveform frequencies,
f_beat = f₁ - f₂ = 12 Hz - 8.0 Hz = 4.0 Hz

Answer 62:
(B) As the index of refraction increases, the angle measured between the light ray and a normal line drawn perpendicular to the surface of the medium decreases. Medium 2 has the smallest angle and therefore the greatest index of refraction. Medium 1 has a slightly larger angle and a slightly smaller index of refraction. Medium 3 has the largest angle and the smallest index of refraction.

Answer 63:
(B) Interference is constructive when the path length difference is a whole number of wavelengths. The second bright maximum occurs at a path length difference of 2λ

Answer 64:
(B) Each of these statements is true.

Answer 65:
(E) During this process,the ice must first melt at a constant temperature according to the formula:

Keep in mind that even though the temperature is given in degrees Celsius,the difference in temperatures is required and the  difference is the same for both the Celsius and Kelvin scales.the sum of melting the ice and then heating the liquid water is 10,000 J.

Answer 66:
(c) For this process, the 10 grams of water (0.01 kg) must be boiled at its boiling temperature of 100°C. The heat required is given by the following formula at that constant temperature:


Answer 67:
(E) Entropy always increases for an isolated system that is reaching equilibrium. This is the second law of thermodynamics.

Answer 68:
(B) The amount of heat, Q, transferred through an object is inversely proportional to the length, L, that that heat must transverse while moving through the object as shown in the equation below.



Answer 69:
(A) Adding heat to a system of gas is positive and removing heat is negative. Doing work on a system is positive while work done by the system is negative. Use the first law of thermodynamics


Answer 70:
(A) The current is directly proportional to the intensity of the light.

Answer 71:
(E) When the frequency of the light is increased, the energy of each photon is increased, E=hf Photons with higher energies will emit electrons with higher kinetic energies, K= hf-  ϕ. The ejected electrons arrive at the opposite plate of the photocell, creating a potential energy and a proportional potential differ­ence between the plates of the photocell.
qV=K
Therefore, increasing the frequency increases both the kinetic energy of the ejected electrons and the resulting voltage of the photocell.

Answer 72:
(E) Fusion results when there is an increase in the atomic number. Hydrogen has an atomic number of 1, and helium has an atomic number of 2. The fusing together of hydrogen atoms produces helium.

Answer 73:
(C) Isotopes have the same elemental symbol but a different number of neutrons. Both of these forms of uranium have the same atomic number, 92, but their masses vary depending upon the number of neutrons. Uranium-238 has 146 neutrons, while uranium-235 has 143 neutrons.

Answer 74:
(D) Adding neutrons adds to only the strong force. Adding neutrons cannot add to the electrostatic force because neutrons have a neutral charge.

Answer 75:
(E) This is the definition of a transistor.
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