A 65 kg crate slides on a rough plane inclined upward at an angle of 28 degrees. The crate is hauled up the plane by lightweight rope that goes parallel to the incline and then over the pulley at the top of the incline. A worker standing below the pulley pulls vertically downward on the rope. If the 55 kg worker hangs his or her entire weight from the rope, it is barely sufficient to move the crate up the incline at a constant velocity of 1.2 m/s.
a) what is the magnitude of the sliding friction force on the box?
b) what is the coefficient of kinetic friction between teh box and the incline?