# Coefficient of static friction of crate

1. Nov 15, 2008

### collegegirl

1. The problem statement, all variables and given/known data
A 200N crate rests on a ramp, the angle is 20 degrees with the horizontal. What is the coefficient of static friction between the crate and ramp surfaces

2. Relevant equations
T=N/cos theta

3. The attempt at a solution
200/cos25 = 219

I don't know where to go from here. The answer is .47 Please show me a direction to take.!!!
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 15, 2008

### asleight

What forces are acting upon the object? (Hint: There are three forces and one of these forces has components if you choose an efficient coordinate system.)

3. Nov 15, 2008

### collegegirl

Would the three forces be gravity, the weight of the crate on the ramp, and the ramp pushing up on the crate? If so, the only one I have numbers for is gravity??

4. Nov 15, 2008

### asleight

Weight and gravity are related by $$\vec{w}=m\vec{g}$$. The other two forces are going to be the frictional force (a function of the normal force) and the normal force, itself, a function of weight. So, where are your x- and y-axes going to lie?