a block rests on an adjustable inclined plane with a max angle before it slips at 21 deg. What is the static coefficient?

Question

Problem:

A 50 N block rests on an adjustable inclined plane; the maximum angle just before it slips is 21 ^o with the horizontal. What is the coefficient of static friction between the block and the plane surfaces?

Secondary Questions I have (Dont have to answer these, but I would appreciate it)

1) What approach should be taken to solve force related problems with only 2 values given?

2) How does the free body diagram look for this?

physics 1.

Answer 1

Sum forces parallel to the ramp to get 50sin21=f (frictional force). 50sin21 = component of W parallel to ramp. Find the component of W normal to the ramp N = 50cos21. The coefficient of static friction = f/N.