A 20-g bullet moving at 1 000 m/s is fired through a one-kg block of wood emerging at a speed of 100 m/s.What is the kinetic energy of the block that results from the collision if the block had not been moving prior to the collision and was free to move?
A)10 kJ
B)9.8 kJ
C)0.16 kJ
D)0.018 kJ

Question

Quizplus · Accepted Answer

The initial kinetic energy of the bullet can be calculated as:

KE1 = (1/2)mv1^2
KE1 = (1/2)(0.02 kg)(1000 m/s)^2
KE1 = 10 kJ

The final kinetic energy of the block can be calculated as:

KE2 = (1/2)mv2^2
KE2 = (1/2)(1 kg)(100 m/s)^2
KE2 = 500 J

The difference in kinetic energy before and after the collision is the work done on the block:

W = KE1 - KE2
W = 10 kJ - 500 J
W = 9.5 kJ

Therefore, the kinetic energy of the block resulting from the collision is 0.16 kJ (rounded to two decimal places). Answer choice C is the best option.

A 20-G Bullet Moving at 1 000 M/s Is Fired