AP Physics C: Mechanics Unit 3 practice questions
Try 10 multiple-choice questions from Unit 3 here. Pick an answer to see why it's right or wrong, then take the timed test above for a full AP-style set.
Question 1
A particle has mass and speed . A second particle has mass and speed . What is the ratio of the second particle's translational kinetic energy to the first particle's translational kinetic energy?
The ratio is
The ratio is
The ratio is
The ratio is
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Answer: (B)
Applying the formula , the new energy is , resulting in a ratio of .
Question 2
An object's momentum magnitude is doubled while its mass remains constant. By what factor does its translational kinetic energy change?
It increases by a factor of
It increases by a factor of
It increases by a factor of
It increases by a factor of
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Answer: (B)
Using the relationship , doubling the momentum () results in , which is a factor of increase.
Question 3
A car starts from rest and accelerates with constant acceleration . If the translational kinetic energy of the car is at time , what is its translational kinetic energy at time ?
The energy is
The energy is
The energy is
The energy is
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Answer: (C)
For constant acceleration from rest, , so velocity doubles when time doubles. Since , doubling velocity quadruples the kinetic energy.
Question 4
An engine delivers constant power to an object starting from rest. By what factor does the object's translational kinetic energy change if the time interval of acceleration is tripled?
It increases by a factor of
It increases by a factor of
It increases by a factor of
It increases by a factor of
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Answer: (A)
Since power is the rate of change of energy (), constant power implies . Therefore, tripling the time triples the kinetic energy.
Question 5
An observer on the ground measures a car's kinetic energy as . A second observer moves in the same direction as the car with half the car's ground speed. What value does the second observer measure for the car's kinetic energy?
The value is
The value is
The value is
The value is
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Answer: (A)
The relative speed is . Since , the new energy is proportional to , which is times the original energy.
Question 6
A particle moves in a circle of radius with constant speed . If the particle moves to a circle of radius while maintaining the same centripetal force magnitude, what is the new translational kinetic energy?
It is half the original energy
It is the same as the original
It is twice the original energy
It is four times the original
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Answer: (C)
Centripetal force is . If is constant and doubles, must also double, meaning doubles.
Question 7
The escape speed from a planet of mass and radius is . A second planet has mass and radius . How does the translational kinetic energy of an object moving at the second planet's escape speed compare to one moving at the first planet's escape speed?
It is half the kinetic energy
It is the same kinetic energy
It is twice the kinetic energy
It is four times the energy
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Answer: (B)
Escape speed squared is proportional to . For the second planet, . Since , the kinetic energy is unchanged.
Question 8
An object of mass starts from rest and is subjected to a net force , where is a constant. How does the object's translational kinetic energy depend on the time ?
The energy is proportional to
The energy is proportional to
The energy is proportional to
The energy is proportional to
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Answer: (D)
Acceleration , so velocity . Kinetic energy , so .
Question 9
A cart of mass moving with speed collides with and sticks to an identical stationary cart. By what factor does the system's total translational kinetic energy change during the collision?
It decreases by a factor of
It decreases by a factor of
It remains exactly unchanged
It increases by a factor of
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Answer: (B)
Conservation of momentum gives . The final energy is , which is half the initial energy.
Question 10
A satellite orbits Earth in a circular path of radius . If the satellite is moved to a circular orbit of radius , by what factor does its translational kinetic energy change?
It decreases by a factor of
It decreases by a factor of
It increases by a factor of
It increases by a factor of
Show answer
Answer: (B)
Orbital velocity squared is . Thus, . Doubling the radius halves the kinetic energy.
What's on the AP Physics C: Mechanics Unit 3 practice test
The standard version takes about 88 minutes and follows the timing and directions of the AP exam, sized to one unit:
- 20 Multiple Choice Questions (40 minutes)
- 1 FRQ – FRQ 1 – Mathematical Routines (24 minutes)
- 1 FRQ – FRQ 2 – Translation Between Representations (24 minutes)
Questions are drawn from 934 multiple-choice questions and 20 FRQs written for Unit 3, Work, Energy, and Power.
Practice AP Physics C: Mechanics Unit 3 FRQs
Answer the unit's free-response questions one at a time and get a score on every part.
- FRQ 1 – Mathematical Routines (6 questions)
- FRQ 2 – Translation Between Representations (3 questions)
- FRQ 3 – Experimental Design (6 questions)
- FRQ 4 – Qualitative/Quantitative Translation (5 questions)