What is (just) the frictional force on the box?

Question

1. A 50 kg box is sliding down a ramp of 30 ^o. The frictional coefficient is k=0.2. What is (just) the frictional force on the box?
2. cos(30 ^o) = 0.866
3. sin(30 ^o) = 0.5

	A.	424.34 N
	B.	160.132 N
	C.	84.868 N
	D.	49 N

Answer 1

The force of friction for a sliding object can be found with F_friction = F_normal * k

So you just need to find F_normal and plug in.

This comes up a lot with inclined planes, so it may be worth writing the formulas in your notebook so you don't have to think it through every time.

1. F_normal = mgcos(θ), where theta is just the angle of the incline.

You should now be able to solve for F_normal, then plug in to find your frictional force.