Posted by Sadi on Monday, January 28, 2013 at 11:03pm.
A 250kg crate is being pushed across a horizontal floor by a force P that makes an angle of 30.8 ° below the horizontal. The coefficient of kinetic friction is 0.224. What should be the magnitude of P, so that the net work done by it and the kinetic frictional force is zero?
Thus far, I know Pcos(30.8) = fk, where fk= (0.224)(mg+Psin(30.8)). I am not sure, however, how I can solve for the magnitude of the P.

Physics  bobpursley, Monday, January 28, 2013 at 11:08pm
no, if the force is pushing up, the term in vertical forces is mgPSin(angle)
P cosTheta=.224(mgPsinTheta)
Now, you know that for net work to be zero, friction has to be zero. which means mgPsinTheta=0
solve for P