A 0.400-kg ball approaches a very massive wall at 20.0 m/s perpendicular to wall and rebounds with 70.0% of its initial kinetic energy. What is the magnitude of the change in momentum of the wall?
A)14.7 kg∙m/s
B)13.6 kg∙m/s
C)2.40 kg∙m/s
D)1.31 kg∙m/s
E)0.00 kg∙m/s

Question

Quizplus · Accepted Answer

The initial momentum of the ball is 0.400 kg * 20.0 m/s = 8.0 kg∙m/s. The final kinetic energy is 70% of the initial, so the final speed is √0.7 * 20.0 m/s ≈ 16.73 m/s. The final momentum is 0.400 kg * 16.73 m/s ≈ 6.69 kg∙m/s. The change in momentum is 8.0 kg∙m/s - (-6.69 kg∙m/s) = 14.7 kg∙m/s.

A 0400-Kg Ball Approaches a Very Massive Wall at 20