Using Newton's laws to solve problems

[juliesangelcleo]

Homework Statement

"while moving in a homeowner is pushing a box across the floor at a constant velocity. The coefficient of friction is .41. The pushing force is directed in a downward motion at and angle of theta below the horizontal. When theta's value is greater then a certain value, then the box can not be moved, no matter the force. What is this theta.

I don't know how to start this one.

 

[denverdoc]

You know that a FBD, and a list of potentially useful eqns is a great way to start. Assuming you have done that, what is the normal force here (the force with which the floor pushes back). From there its easy to get the frictional force. The push must of course be resolved into X and Y components.