A 39- kg girl standing at rest on slippery (frictionless) ice catches a 1- g ball moving at 10 m/s. Just afterward, the girl is
A) moving at 0.5 m/s.
B) moving at 2 m/s.
C) moving at 0.25 m/s.
D) moving at 4 m/s.
E) at rest.

Question

Quizplus · Accepted Answer

Using conservation of momentum, the initial momentum of the system is equal to the final momentum. The initial momentum is the momentum of the ball (0.001 kg * 10 m/s = 0.01 kg*m/s). The final momentum is the combined mass of the girl and the ball (39 kg + 0.001 kg) times the velocity of the girl. Solving for the velocity gives approximately 0.25 m/s.

A 39- Kg Girl Standing at Rest on Slippery (Frictionless)