A science teacher uses the following experiment to show her students the influence of elastic materials on collisions. She released from rest a 125 g cube on a smooth incline, making an angle of 15°. The cube slides 75 cm, hits a super-elastic material placed at the lowest part of the incline, and then goes up 45 cm along the incline. The contact time between the cube and the elastic material is measured to be 75 ms by an ultrasensitive motion detector. Find the mean force exerted by the cube on the elastic material.