Ou are lowering two boxes, one on top of the other, down a ramp by pulling on a rope parallel to the surface of the ramp (fig. e5.33). both boxes move together at a constant speed of 15.0 cm> s. the coefficient of kinetic friction between the ramp and the lower box is 0.444, and the coefficient of static friction between the two boxes is 0.800. (a) what force do you need to exert to accomplish this