A 22.3-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 change in the kinetic energy of the bullet-block system as a result of the collision assuming the block is free to move?
A)0 J
B)10.8 kJ
C)-10.8 kJ
D)11.2 J
E)223 J

Question

Quizplus · Accepted Answer

The initial kinetic energy of the bullet is (1/2)(0.0223 kg)(1000 m/s)^2 = 11 150 J. 
The final kinetic energy of the bullet is (1/2)(0.0223 kg)(100 m/s)^2 = 111.5 J. 
The initial kinetic energy of the block is 0 J since it starts at rest. 
The final kinetic energy of the block is (1/2)(1 kg)(100 m/s)^2 = 5000 J. 
The change in kinetic energy of the bullet-block system is therefore (111.5 + 5000) - 11 150 = -10 838.5 J, which is approximately -10.8 kJ (rounded to one decimal place). Since the kinetic energy decreases, the answer is negative.

A 223-G Bullet Moving at 1 000 M/s Is Fired Through