posted by craig45 .
A ball of mass 0.70 kg moving with speed of 1.0 m/s hits a wall and bounces back with the same speed in the opposite direction. What is the change in the ball's kinetic energy?
The speed doesn't change. What does that tell you?
If you don't know, review the definition of kinetic energy:
(1/2) M V^2
Even if the velocity changes sign, V^2 does not change sign.
The mass M doesn't change, either.