Question

A 1205 kg car is running a speed of 35 m/s along a level road. How large a constant retarding force is required to stop it in 15 s? 

Answer 1

The Newton's second law says

$$F=ma=m\frac{\Delta v}{\Delta t}$$

$$F=1205\times \frac{0-35}{15}=-2812\:\rm N$$