A 40-kg girl,standing at rest on the ice,gives a 60-kg boy,who is also standing at rest on the ice,a shove.After the shove,the boy is moving backward at 2.0 m/s.Ignore friction.The girl's speed is
A)zero
B)1.3 m/s
C)2.0 m/s
D)3.0 m/s
E)6.0 m/s

Question

Quizplus · Accepted Answer

According to the conservation of momentum, the total momentum before and after the shove must be equal. Initially, both are at rest, so the total momentum is zero. After the shove, the boy's momentum is 60 kg * 2.0 m/s = 120 kg*m/s. To conserve momentum, the girl's momentum must be equal and opposite, so 40 kg * v = 120 kg*m/s, giving v = 3.0 m/s.

A 40-Kg Girl,standing at Rest on the Ice,gives a 60-Kg