Question

A driver in a 1000 kg car traveling at 13 m/s slams on the brakes and skids to a stop. if the coefficient of friction between the tires and the horizontal road is 0.80, how long will the skid marks be?

Answer 1

Using F = ma to the direction of travel;

-F = 1000 * a 

-F is due to the reverse direction of the frictional force. 

F = 0.8 * 1000 * 9.81 = 7250 N 
-7850 = 1000 * 9 
9 = -7.85m/s^2

Using V^2 = U^2 + 2aS to the direction of trabel 

0 = 20^2 + 2(-7.85)S 

S = 25.5m 

So the skid marks will be there for 25.5 which estimated is 26m. 

The correct answer is 26m. 

I hope this helps you out!