# Homework Help: Find the Coffiecient of Rolling Friction

1. Oct 9, 2006

### kenau_reveas

Information given:

Two bicycle tires are set rolling with the same initial speed of 3.60 m/s along a long, straight road, and the distance each travels before its speed is reduced by half is measured. One tire is inflated to a pressure of 40 {\rm psi} and goes a distance of 18.1 m; the other is at 105 {\rm psi} and goes a distance of 93.1 m. Assume that the net horizontal force is due to rolling friction only and take the free-fall acceleration to be g = 9.80 m/s^2.

Question 1:

What is the coefficient of rolling friction mu_r for the tire under low pressure?

2. Oct 9, 2006

### OlderDan

Here are some clues
You know the velocity change and the distance it took for that change to occur. Can you find the acceleration? Once you know the acceleration, you can find the force that was acting to slow the tire. This is the frictional force, which is a fraction of the normal force. The fraction is called the coefficient of friction. On a flat surface, the normal force is simply related to the weight of the object.

3. Oct 9, 2006

### kenau_reveas

i can find acceleration..but no clue after that..

4. Oct 9, 2006

### OlderDan

F = ma
You don't know the mass, but in the end it will cancel. From the acceleration you know the frictional force. You also kow that the frictional force is proportional to the normal force and the mormal force is proportional to the weight (which is proportional to the mass). If you turn these statements into the appropriate equations, the mass will divide out and you will find the answer.