50. A body rests on a rough horizontal plane. A
force is applied to the body directed towards
the plane at an angle Q with the vertical. The
body can be moved along the plane
(a) only if Q is more than the angle of friction
(b) only if Q is less than the angle of friction
(c) only if Q is equal than the angle of friction
(d) for all values of Q
(e) none of the above