Question

A car is travelling 64km/h in a 50km/h zone. The driver notices a photo radar camera 100 m down the road and slows down. To reach the speed limit at the moment the car reaches the camera, the acceleration of the car must be?

Answer 1

The acceleration must be

$$a=\frac{v_f^2-v_i^2}{2d}=\\\space\\ =\frac{(50\cdot\frac{1000}{3600})^2-(64\cdot\frac{1000}{3600})^2}{2\cdot100}=-0.62\text{ m/s}^2.$$