Question

A motorist is travelling at 15 m/s when he sees a child run into the road. He brakes and
the car comes to rest in 0.75 s.
b) The deceleration of the car is?

Answer 1

The acceleration of the car

$$a=\frac{v_f-v_i}{t}=\frac{0-15}{0.75}=-26.7\:\rm m/s^2$$