Question

Two cars are traveling along a straight line in the same direction, the lead car at 25.0 m/s 

and the other car at 30 m/s. At the moment the cars are 40 m apart, the lead driver applies the 

brakes, causing her car to have an acceleration of -2.00 m/s2

. 

(a) How long does it take for the lead car to stop

Answer 1

The time required for the lead car to stop is

$$t=\frac{v}{a}=\frac{-25}{-2}=12.5\text{ s}.$$