# Homework Help: Coefficient of friction for a car sliding down an icy hill

1. Sep 26, 2011

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

A car is sliding down an icy hill inclined at 1.6 degrees, find the coefficient of friction.

2. Relevant equations

f_k=\mu_k*n

3. The attempt at a solution

Don't know how to begin it only given the angle of the hill.

2. Sep 26, 2011

### omoplata

Draw a free body diagram of the car. Mark all the forces on it. Then apply Newton's laws of motion.

3. Sep 26, 2011

### PeterO

If you do all the manths with component, you will find that the co-efficient of static friction is the tangent of the angle of the hill when the body is on the point of slipping.
One problem with this question is we don't know if this is the smallest angle for which it will slip?

If it slips at 1.6 degrees, it will certainly slip at 10 degrees, but did it slip and 1.5? 1.4? 1.3 ? ...

Also I noted that your forumula had the subscript k - presumably meaning the kinetic [moving situation] If the car is sliding down the hill but NOT accelerating, then tan1.6 will give the co-efficient you seek. However, we are not told whether it is accelerating or not???

4. Sep 27, 2011

### omoplata

PeterO is right. This problem cannot be solved without knowing the acceleration of the car.

5. Sep 27, 2011