An object hits a wall and bounces back with half if its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy? I am not sure I understand the question, is it 1:2? A ball drops some distance and gains 30 J of kinetic energy. Do not ignore air resistance. How much gravitational potential did the ball lose? I would say more than 30J since we have to take air resistance into consideration. Thanks!