A ball with original momentum +7.0 kg⋅m/s hits a wall and bounces straight back without losing any kinetic energy.The change in momentum of the ball is:

Question

Quizplus · Accepted Answer

The change in momentum is equal to the final momentum minus the initial momentum. Since the ball bounces straight back without losing any kinetic energy, the final momentum will be equal in magnitude but opposite in direction to the initial momentum. Therefore, the final momentum will be -7.0 kg⋅m/s. 
Change in momentum = final momentum - initial momentum
Change in momentum = (-7.0 kg⋅m/s) - (+7.0 kg⋅m/s) 
Change in momentum = -14 kg⋅m/s, which is choice D.

A Ball with Original Momentum +7