# Help with a homework question

1. Jul 17, 2007

### saikamaniac

Friction provides the centripetal force necessary for a car to reval around a circular flat racetrack. What ios the maximum speed at which a car can travel safely around a track of radius 80m if the coefficient of friction between the tyres and road is 0.3?

I really have no idea how to attempt this question...

2. Jul 17, 2007

### HallsofIvy

Staff Emeritus
Do you know how to calculate the "centrifugal force" on the car? The friction force, equal to 0.3 times the weight of the car, must be equal to that.

3. Jul 17, 2007

### saikamaniac

well the centrifugal force is just equal but opposite to the centripetal force
which i don't know...and i dont know the MASS of the car and thus cant calculate the weight

4. Jul 17, 2007

### GoldPheonix

A common thing for people who are just starting physics is to forget that, often times, mass is irrelevant to finding a solution.

The centrifugal forces must equal friction, correct? What do you do when two equations equal each other?

Whenever I get stuck, I like to just starting writing off my known equations:

$$\Sigma F_c = m\frac{v^2_t}{r}$$

$$F_f = \mu m g$$