Coeffiecent of Kinetic Friction Problem

[c.melissas]

1. A car is traveling at 15 meters/second on a horizontal road. The brakes are applied and the car sids to a stop in 4 seconds. The coefficient of kinetic friction between the tires and the road is



2. Coefficient of kinetic friction = friction / Normal Force



3. Time to stop / Velocity = 4/15 = .2666. The correct answer is roughly .38, but I have no idea on how to arrive at that.

 

[PhanthomJay]

1. A car is traveling at 15 meters/second on a horizontal road. The brakes are applied and the car sids to a stop in 4 seconds. The coefficient of kinetic friction between the tires and the road is



2. Coefficient of kinetic friction = friction / Normal Force



3. Time to stop / Velocity = 4/15 = .2666. The correct answer is roughly .38, but I have no idea on how to arrive at that.

Where does this equation come from? v = at. Solve for a, then apply Newton's 2nd law to the car.

 

[c.melissas]

Thanks for the help. I really had no idea how to answer this problem. I am confused on what do after solving for acceleration because I could not find a way to determine the force or the mass of the car.

 

[PhanthomJay]

You may not need to know the mass, write out Newton's 2nd for the car. The force acting on the car is the friction force, which is slowing it down (decelerating it) to a stop.
And by the way,welcome to PF!

 

[c.melissas]

Thank you, and I was able to figure it out.