AP Physics 1 Question 130: Answer and Explanation

Question: 130

10. In Collision A, two carts collide and bounce off each other. In Collision B, a ball sticks to a rigid rod, which begins to rotate about the combined center of mass. Which of the following statements about quantities in each collision is correct?

• A. Collision A: each cart experiences the same force, time of collision, and change in kinetic energy. Collision B: the ball and the rod each experience the same torque, time of collision, and change in rotational kinetic energy.
• B. Collision A: each cart experiences the same force, time of collision, and change in linear momentum. Collision B: the ball and the rod each experience the same torque, time of collision, and change in angular momentum.
• C. Collision A: each cart experiences the same force, time of collision, and change in kinetic energy. Collision B: the ball and the rod each experience the same torque, time of collision, and change in angular momentum.
• D. Collision A: each cart experiences the same force, time of collision, and change in velocity. Collision B: the ball and the rod each experience the same torque, time of collision, and change in angular velocity

Correct Answer: B

Explanation:

B-The problem says nothing about the collision being "elastic"; therefore, the change in kinetic energy of any sort does not have to be the same for each object. Velocity is never conserved in a collision-momentum is-so Choice D is ridiculous. Newton's third law demands that the force of one cart on another is the same, and so also the torque on each object about the center of mass.