# Need help finding coefficient of kinetic friction

1. Jul 23, 2008

### zinniagirl

1. The problem statement, all variables and given/known data
A horizontal force of 150 N is used to push a 40.0 kg packing crate a distance of 6.00 m on a rough horizontal surface. If the crate moves at constant speed, find the coefficient of kinetic friction between the crate and the surface.

2. Relevant equations
fK= coeff. of kin. friction X N
Fy= -mgy + normal force

3. The attempt at a solution
I started by using Fy= -mgy + N to be 0= -40 (9.8) (cos 0) + N and found N be 392. But now I'm not sure where to go from here to find the coefficient of kinetic friction. Can anyone help?

2. Jul 23, 2008

### rock.freak667

Constant speed means the resultant force is zero....so what is the value of the frictional force?

3. Jul 23, 2008

### zinniagirl

150 N. So the coefficient of kinetic friction would then be .38, correct?

4. Jul 23, 2008

### rock.freak667

Yes that should be correct.

5. Jul 23, 2008

Thanks!