Question: 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 at an angle theta below the horizontal on the crate with a force \vec F.

Part A: What magnitude of force \vec F is required to keep the crate moving at constant velocity?

Part 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.

I want help to find what magnitude of force \vec F is required to keep the crate moving at constant velocity.