You are lowering two boxes, one on the top of the other, down the ramp shown in the figure by pulling on a rope parallel to the surface of the ramp. Both boxes move together at a constant speed of 15cm/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?
b- what are the magnitude and direction of the friction force on the upper box?