Question

A 1.20*10^2 kg crate is being pushed across a horizontal floor by a force P that makes an angle of 30.0° below the horizontal. The coefficient of kinetic friction is 0.350. What should be the magnitude of P, so that the net work done by it and the kinetic frictional force is zero?

Answer 1

So P is pointing UP?

If so, a portion of P counters weight, and in so doing, reduces friction to zero.

Psin30=mg
P= 2mg

Answer 2

If the net force is zero, the friction force balances the horizontal component of the applied force P.

Calculate the Friction force and divide it by cos 30.

The fact that the applied force is 30 deg below horizontal will affect the friction force.

Answer 3

My interpretation of the problem is different from Bob's. I did not assume that the friction was reduced to zero, only that it balances the applied force to make the net force (and work) zero.