A large crate with mass m rests on a horizontal floor. The coefficients of friction between the crate and the floor are μs and μk. A woman pushes downward with a force
→
F
on the crate at an angle θ below the horizontal. (a) What magnitude of force
→
F
is required to keep the crate moving at constant velocity? (b) If μs is greater than some critical value, the woman cannot start the crate moving no matter how hard she pushes. Calculate this critical value of μs.