# Homework Help: Physics 20, Friction.

1. Apr 1, 2009

### SimonJ

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

I need to find the coefficient of friction on a surface. Two weights were given, 0.5672kg and 0.050kg

2. Relevant equations

m1a + Mm1g = m2g - m2a

3. The attempt at a solution

(0.5672kg)a + M (0.5672)(9.81) = (0.050kg)(9.81) - (0.050kg) a

M represents the coefficient of friction. I need to solve for that, I just don't know where to take it from here.

2. Apr 1, 2009

### mgb_phys

That's not enough of a question - what were the two weights doing?

3. Apr 1, 2009

### SimonJ

That is what is happening

4. Apr 1, 2009

### mgb_phys

That helps.
Now try drawing in the forces.
The frictional force is = coeff_friction * normal force (ie weight)

5. Apr 1, 2009

### SimonJ

Can you explain that a little more please?

6. Apr 1, 2009

### mgb_phys

There is a force down on the 0.05kg mass = m g
This same force pulls the larger mass to the right, so an equal friction force acts to the left (assuming no loss in the pulleys).
The definition of coeeficient of friction is
friction force = coeef * normal force

The normal force is the force acting down on the suface = M g

Last edited: Apr 2, 2009
7. Apr 2, 2009

Ok thanks!