Question

A body of mass 6N rest on a plane inclined at 30 degree to horizontal.
a) what force keeps it from sliding down on the plane?
b) what is the coefficient of the friction?

Answer 1

1) Holds the force of friction.

2)

$$F = \mu N$$ $$\mu = F/N$$ $$\mu = {mg\sin\alpha \over N} = {mg\sin\alpha \over mg\cos\alpha } = \tan \alpha$$

$$\mu = \tan 30^o$$

$$\mu = \sqrt{3} / 3 = 0.577$$

Answer: 1) friction force; 2) 0.577