# Finding Applied Force from Coefficient of Friciton and mass

1. Sep 6, 2013

### jmcpherson82

You are pushing horizontally on a 3.0 kg box of wood, pressing against a wall. If the coefficient of static friction is 0.60, how much force must you exert on the block to prevent it from sliding down?

1. The problem statement, all variables and given/known data
What is the force applied to keep the box from sliding down?

m= 3.0kg
u= o.60
g=9.81

2. Relevant equations

FF=uFn
Fnet = ma

3. The attempt at a solution

I tried to use the equation FF=uFn:

FF = .6(3)(9.81)
FF=17.658 N

Am I doing this correct?

2. Sep 6, 2013

### Staff: Mentor

Hi jmcpherson82. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

The vertical forces must balance. The upward force due to friction = 0.6 Fn

Last edited by a moderator: May 6, 2017
3. Sep 6, 2013

### jmcpherson82

So how would I find Fnet without acceleration? Because then I can't do the equation Fnet = ma

4. Sep 6, 2013

### Enigman

Fnet=0
EDIT: Oh, N.O.'s talking about normal force not net force.

5. Sep 6, 2013

### Staff: Mentor

The upward force = the downward force

The upward force is due to friction.