A driver in a 1000.0 kg car traveling at 20 m/s slams on the brakes and skids to a stop. If the coefficient of friction between the tires and the
road is 0.80, how long will the skid marks be?
A) 26 m
B) 21 m
C) 33 m
D) 24 m
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 = 7850 N`
`-7850 = 1000*a`
`a = -7.85m/s^2`
Using `V^2 = U^2+2aS` to the direction of travel
`0 = 20^2+2*(-7.85)S`
`S = 25.5 m`
So the skid marks will be there for 25.5m `~~` 26m.
The correct answer is A).