# Homework Help: Static force/Static friction

1. Nov 1, 2011

1. The problem statement, all variables and given/known data

Suppose a block of mass = 10kg is on an incline plane that makes an angle = 45° from the horizontal. If a force of 10 N is being applied to the block, downward, and perpendicular to the surface, and the block is not moving, what is the static force of friction? What is the coefficient of static friction?

2. Relevant equations

$\mu$$_{}s$ = Fn

3. The attempt at a solution

$\mu$$_{}s$ = FN

Am I on the right track?

Last edited: Nov 2, 2011
2. Nov 1, 2011

### PhanthomJay

should be N -mgcos45 -10 = 0, N = mgcos45 +10. Don't confuse the normal force, N, with the force unit of Newtons (N)!!!
This is the correct answer for the first part.
you mean $F_f$ is less than or equal to $\mu_sN$, don't you?

3. Nov 1, 2011

LOL Yes, I did mean that. So it will be $\mu$$_{}s$ = Ff / N?

Which will be 69.3N/79.3N..correct?

4. Nov 1, 2011

### PhanthomJay

No-o. Since static friction force is always less than or equal to $\mu N$ , then $\mu$$_{}s$ is greater than or equal to Ff / N.

5. Nov 1, 2011