# Help help

1. Oct 25, 2006

### allblonde

Coefficient of kinetic friction

so im working on the force of friction and overcoming friction
i know that the coeffcient of friction is equal to the kinetic force over the normal force and i can get these when hte system is on a horisantal surface
But i dont understand how to get them with an incline

Problem: a box slides down a 30 degree ramp with an acceleration of 1.2 m/s squared. Determine the coefficient of kinetic friction between the box and the ramp.

im not sure i even know where to start, well i have a free body diagram

Last edited: Oct 25, 2006
2. Oct 25, 2006

### allblonde

ok so i got that the force perpendicular (x) - (subtract) the force of friction = mass*acceleration of x
but the question does not give you a mass!
how do i determine the normal force if i don't have a mass?

3. Oct 25, 2006

### Dorothy Weglend

What is the acceleration down the ramp with no friction?

Dorothy

4. Oct 25, 2006

### allblonde

um it says 1.2 m/s squared

5. Oct 25, 2006

### Dorothy Weglend

That is WITH friction. What is it without friction?

6. Oct 25, 2006

### allblonde

how do i find that out? i dont know what the force of friction is in this problem

7. Oct 26, 2006

### Dorothy Weglend

Well, let me put it to you this way. You have a freebody diagram. What are your force equations? Let's take a look at those.