A bullet of mass 0.010 kg and speed of 500 m/s is brought to rest in a wooden block after penetrating a distance of 0.10 m. The work done on the bullet by the block is
A) -1250 J.
B) 1250 J.
C) -2.5 J.
D) 2.5 J.
E) zero.

Question

Quizplus · Accepted Answer

The work done on the bullet by the block is equal to the change in kinetic energy of the bullet. The initial kinetic energy is (1/2)mv^2 = (1/2)(0.010 kg)(500 m/s)^2 = 1250 J. Since the bullet is brought to rest, the final kinetic energy is 0 J. Therefore, the work done is -1250 J (negative because the block does work on the bullet to stop it).

A Bullet of Mass 0