Calculating Static Frictional Force on an incline

[Shadow236]

Homework Statement

A car (m = 1680 kg) is parked on a road that rises 17° above the horizontal. What are the magnitudes of (a) the normal force and (b) the static frictional force that the ground exerts on the tires?

Homework Equations

F_s^MAX = Mu*F_N or in this case: F_s^MAX = Mu*mg*cos(17)

The Attempt at a Solution

I found (a), the normal force by finding mg (1680 * 9.8) and then multiplying that by cos(17) because of the incline. My problem is finding the static frictional force because there is no coefficient given. I've tried to find the coefficient by using the normal force, but I still end up with two unknowns... 16464 (F_N) = F_s/Mu.

 

[Doc Al]

I found (a), the normal force by finding mg (1680 * 9.8) and then multiplying that by cos(17) because of the incline.

Good.

My problem is finding the static frictional force because there is no coefficient given. I've tried to find the coefficient by using the normal force, but I still end up with two unknowns... 16464 (F_N) = F_s/Mu.

You are asked to find the actual static friction force, not the maximum value between the surfaces. Hint: You don't need the coefficient, just the conditions for static equilibrium.

 

[voko]

Because the car is parked, it is stationary, that is to say, in equilibrium. So the force of static friction is balanced by some other force. What is this force? Can you find it?

 

[Shadow236]

Because the car is parked, it is stationary, that is to say, in equilibrium. So the force of static friction is balanced by some other force. What is this force? Can you find it?

Are they the Normal Force and the weight of the car?

 

[voko]

Isn't the normal force perpendicular to the force of friction? How can they balance each other then?

It is probably best to list all the forces, choose a coordinate system, and write down the equations of equilibrium.