# Frictional Forces and 1D Motion

• Peterson
In summary, the specific problem given is to find the minimum time and distance for a car to come to a stop on a wet concrete road with a coefficient of kinetic friction of 0.5. To solve this, the equation for stopping with a negative acceleration is needed, and it is noted that the braking force is constant regardless of initial speed. The stopping distance is dependent on velocity, but it can be predicted using the weight and coefficient of friction.

#### Peterson

INTRODUCTION:
This is a problem from my Introduction to Physical Science class using "Conceptual Physics" 10th Ed.by Paul G. Hewitt

EXACT PROBLEM:
"The coefficient of kinetic friction between a rubber tire and a wet concrete road is 0.5."

PROBLEMS FACED:
a) Find the minimum time in which a car whose initial speed is 30 mi/hr can come to a stop on such a road.
b) What distance will the car cover in this time?

MY THOUGHTS:
I know I have a coefficient of friction & V0 and Vf. Beyond that, I don't know how to look for the time it will take. What equation am I supposed to be using?

Lets take this a step at a time. To stop, you need a negative acceleration. Assume the brakes are aplied full force as in panic stop.

I still find the fact that speed/velocity never enters the eqn curious: that is the braking force is constant. Whether from 100mph or 5mph the retarding force is the same. So its like a baseball thrown upwards at different speeds.:The stopping distance depends on velocity, but its predictable. This is key.

So in a horizontal position, the frictional force depends on the negative force/acceleration generated by the weight times the coeffiecient of friction. Any help?

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