Acar is traveling 20 m s when the driver sees a child standing in the road. he takes 0.8 seconds to react, then steps on the brakes and slows down at 7.0 m/s squared. how far does the car go before it stops?

We use kinematic equations,

During reaction time,

                       (A)

During the deceleration,

.                                   (B)

Here, u is initial velocity, v is final velocity , a is acceleration and t is time.

There is no deceleration during his 0.8 sec reaction time so a=0, from equation (A),

During the deceleration (a = -7.0 m/s^2) ,  final velocity will be zero i.e v = 0, therefore from equation (B),

Thus, the distance traveled by car after he sees need to put brakes is

mass and volume are the answers you are looking for