An object hits a wall and bounces back with half of its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy?
A) 1/2
B) 1/4
C) 2
D) 4
E) 8

Question

Quizplus · Accepted Answer

The kinetic energy of an object is proportional to the square of its speed. If the object bounces back with half of its original speed, its final speed will be 1/2^1/2 times its initial speed. Thus, its final kinetic energy will be proportional to its final speed squared, which is (1/2^1/2)^2 = 1/2. Therefore, the ratio of the final kinetic energy to the initial kinetic energy is 1/2 divided by 1, which is 1/2 or 0.5. Answer B is the only option that matches this result.

An Object Hits a Wall and Bounces Back with Half