# Bar of soap

1. Oct 3, 2004

### strugglin-physics

A wet bar of soap slides freely down a ramp 9.35 m long inclined at 7.00°. How long does it take to reach the bottom? Assume muk = 0.0550.

Okay I've got my x & y componants
9.35cos(7)=9.28
9.35sin(7)=1.14

But now what since I don't have the mass of the soap or the acceleration, what do I do next?

2. Oct 3, 2004

### e(ho0n3

Draw yourself a free-body diagram of the situation. It should be pretty clear to you from then on.

3. Oct 3, 2004

### strugglin-physics

Okay I drew my FBD but I still don't know how much time it would take the soap to slide down the ramp. Maybe I'm missing something.
I have the frictional force going NW the normal force going NE and the weight force going South... is that right?

4. Oct 3, 2004

### e(ho0n3

Yes. Set up the equations using Newton's 2. law, solve for the acceleration and use some kinematics to solve for time.

5. Oct 3, 2004

### strugglin-physics

How do I solve for acceleration if the mass is unknown?

6. Oct 3, 2004

### arildno

Well, but since the frictional force, the gravity and the "ma" terms are all proportional to the mass, it's a common factor which you can eliminate
(the solution is independent of the mass)