# Distance needed for the car to stop

1. Oct 3, 2004

### lovelylemon

"A car is traveling at 70.4 m/h on a horizontal highway. The acceleration of gravity is 9.8 m/s^2. If the coefficient between the road and tires on a rainy day is 0.052, what is the minimum distance in which the car will stop?"

I can't figure out how to solve this problem. To find the frictional force, I need the normal force, and to find the normal force I need the mass right?

2. Oct 3, 2004

### modmans2ndcoming

is the car traveling in meters per hour or miles per hour. your unit notation is ambiguous. but anyway. with the information give, you either have to derive the information from the information you have, in which case you would need to figure out how the coefficient of friction was calculated which should give you the cars mass, or mass will not play a part in this because you have been given all the information you need to calculate the unknowns.

3. Oct 3, 2004

### geometer

In this case, where the force is parallel (actually anti-parallel, but taking just the magnitude you can ignore this) to the distance travelled, work is defined as force times distance. And by the work energy theorem, work is also defined as the change in kinetic energy; kinetic energy final minus kinetic energy initial. Set this equation up, remember that the force in the work equation is due to friction and you should be able to work it from there.