Question

How to take correct direction of friction in block on inclined plane?

Answer 1

You have a block with mass m that is initially at rest. The block sits on a surface at angle θ to the ground, has coefficient of kinetic friction μk, and a coefficient of static friction μs. There is an external force F acting on the block parallel to the ground. I am wondering, if you are given this setup, how to determine the direction of friction without first determining the direction of motion?

In this case the external force opposes the force of gravity.