# How to find coefficient of friction?

1. Nov 12, 2007

### Narayanswamy

If a driver traveling down an 8% grade hill slams down the brakes of his car and skids 30 meters, what is the coefficient of friction ( assuming he was traveling at 25 MPH or more)?

2. Nov 12, 2007

### fliinghier

you use the acceleration due to gravity and say that the friction overcomes that by ___ amount

Last edited: Nov 12, 2007
3. Nov 12, 2007

### Narayanswamy

What is 8% gradient in degrees?

4. Nov 12, 2007

### Narayanswamy

is Coefficient of friction tan(slope in degrees) ?

5. Nov 12, 2007

### fliinghier

i believe that 8% is the tangent of the angle. the coefficient of friction is mu, and for most cars should be between .6 and .8

6. Nov 13, 2007

### Staff: Mentor

Assemble the usual suspects: Draw a diagram showing all the forces acting on the car. Apply Newton's 2nd law to relate the net force to the acceleration. Use kinematics or work/energy to compute the acceleration. (Pick a specific speed: convert 25 mph to m/s.)