Question

A car of mass 2400 kg moving with a velocity of 20 m s⁻¹ is stopped in 10 seconds on applying brakes. Calculate the retardation and the retarding force.

Answer 1

Let us first calculate the retardation $=\frac{\left(v-u\right)}{t}$
$$\begin{gathered} =\frac{\left(0-20\right)}{10} \\ =\frac{-20}{10} \\ =\frac{-2\cancel{0}}{1\cancel{0}} \\ =-2\mathrm{m}/{\mathrm{s}}^2 \end{gathered}$$

Now, we are going to find retarding force = mass × acceleration
= 2400 kg × −2
= −4800 N
The negative sign implies that the force on the car is acting opposite to the motion of the car.