Question

When a car driver travelling at a speed of 10 m/s applies brakes and brings the car to rest in 20 s, then retardation will be:

(a) + 2 m/s²
(b) − 2 m/s²
(c) − 0.5 m/s²
(d) + 0.5 m/s²

Answer 1

(d) The term “retardation” means negative acceleration.
Initial velocity = 10 m/s
Final velocity = 0 m/s
Time taken = 20 s
$$\begin{gathered} \mathrm{Acceleration}=\frac{0-10}{20} \\ \Rightarrow \mathrm{Acceleration}=-0.5\mathrm{m}/{\mathrm{s}}^2 \\ \Rightarrow \mathrm{Retardation}=0.5\mathrm{m}/{\mathrm{s}}^2 \end{gathered}$$