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AP Physics C: Mechanics Practice Quiz: Elastic and Inelastic Collisions

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 10 questions to check your progress.

Question 1 of 10

Which of the following statements best describes an elastic collision?

All Questions (10)

Which of the following statements best describes an elastic collision?

A) The initial kinetic energy of the system is equal to the final kinetic energy.

B) The objects stick together and move with the same velocity.

C) The total kinetic energy of the system decreases.

D) The final kinetic energy of the system is greater than the initial kinetic energy.

Correct Answer: A

Based on the provided content, an elastic collision is explicitly defined as one in which the initial kinetic energy of the system is equal to the final kinetic energy of the system.

In a perfectly inelastic collision, what is the defining characteristic of the objects' motion after the interaction?

A) They move in opposite directions with equal speeds.

B) They come to a complete stop.

C) They stick together and move with a common velocity.

D) Their total kinetic energy remains unchanged.

Correct Answer: C

The provided content states that in a perfectly inelastic collision, the objects stick together and move with the same velocity after the collision.

A system of two objects undergoes an inelastic collision. Which of the following must be true about the system's total kinetic energy?

A) It increases.

B) It decreases.

C) It remains constant.

D) It becomes zero.

Correct Answer: B

The definition of an inelastic collision provided is one in which the total kinetic energy of the system decreases.

Two clay balls collide and merge into a single lump. How would an observer describe this interaction based on the provided definitions?

A) As an elastic collision, because mass is conserved.

B) As a perfectly inelastic collision, because the objects stick together.

C) As an elastic collision, because the objects are made of the same material.

D) As an inelastic collision, but not perfectly inelastic.

Correct Answer: B

The scenario describes objects sticking together after a collision, which is the specific definition of a perfectly inelastic collision according to the provided text.

An experimenter measures the total kinetic energy of a two-object system to be 75 J before a collision and 60 J after the collision. What type of collision has occurred?

A) Perfectly inelastic

B) Inelastic

C) Elastic

D) It is impossible to determine from the information given.

Correct Answer: B

The content defines an inelastic collision as one where the total kinetic energy of the system decreases. Since the kinetic energy decreased from 75 J to 60 J, the collision is inelastic.

Which statement correctly distinguishes a perfectly inelastic collision from other types of inelastic collisions?

A) Only in a perfectly inelastic collision is kinetic energy lost.

B) In a perfectly inelastic collision, the objects stick together, which is not necessarily true for all inelastic collisions.

C) A perfectly inelastic collision is the only type where the final velocity is zero.

D) Kinetic energy is conserved in a perfectly inelastic collision but not in other inelastic collisions.

Correct Answer: B

All inelastic collisions involve a decrease in kinetic energy. The specific characteristic of a *perfectly* inelastic collision, as stated in the content, is that the objects stick together and move with a common velocity.

What is the primary condition used to determine if an interaction between objects is elastic?

A) The objects stick together after the collision.

B) The objects move apart after the collision.

C) The initial kinetic energy of the system equals the final kinetic energy.

D) The total kinetic energy of the system decreases.

Correct Answer: C

According to the provided text, the defining condition for an elastic collision is that the initial kinetic energy of the system is equal to the final kinetic energy of the system.

A billiard ball strikes another stationary billiard ball. After the collision, the balls move off separately. A measurement shows that the total kinetic energy of the two-ball system is slightly less after the collision than before. This interaction is best described as:

A) Elastic

B) Inelastic

C) Perfectly inelastic

D) Not a collision

Correct Answer: B

The problem states that the total kinetic energy decreased, which is the definition of an inelastic collision. It is not perfectly inelastic because the objects did not stick together.

What quantity is conserved in an elastic collision that is NOT conserved in an inelastic collision, according to the provided text?

A) The number of objects in the system.

B) The total mass of the system.

C) The total kinetic energy of the system.

D) The direction of motion of the system.

Correct Answer: C

According to the provided definitions, the key distinction between elastic and inelastic collisions is the conservation of total kinetic energy. It is conserved in elastic collisions but decreases (is not conserved) in inelastic collisions.

If a collision occurs in which the objects stick together, but a measurement reveals that the total kinetic energy of the system remained constant, how would this be classified based on the provided definitions?

A) As a perfectly inelastic collision because the objects stick together.

B) As an elastic collision because kinetic energy is constant.

C) As both elastic and perfectly inelastic.

D) This scenario presents a contradiction between the provided definitions.

Correct Answer: D

The provided text defines a perfectly inelastic collision as one where objects stick together, which is a type of inelastic collision where kinetic energy decreases. It defines an elastic collision as one where kinetic energy is constant. A scenario where objects stick together AND kinetic energy is constant contradicts these separate definitions.