...A ball of mass

Question

A ball of mass 7.91 kg moving with speed 5.86 m/s hits a wall and bounces back with speed 6.19 m/s in the opposite direction. What is the change in the ball’s kinetic energy?

Answer 1

Change in kinetic energy ΔKE = 1/2 m (v_f² - v_i²) = 3.95₅ (38.3₂ - 34.3₄) = +15.7 J. The wall ADDED energy to the ball!