Question

Find the initial velocity of a car which is stopped in 10 seconds by applying brakes. The retardation due to brakes is 2.5 m/s².

Answer 1

Retardation due to brakes = 2.5 m/s²​

$\therefore$ a = $-$2.5 m/s²

Time taken in stopping = 10 seconds

Final velocity of car = 0 m/s

Let the initial velocity = u

Using the first equation of motion, v = u +at

$$\begin{gathered} \Rightarrow 0=u+(-2.5\mathrm{m}/{\mathrm{s}}^2)\times 10\mathrm{s} \\ \Rightarrow u=25\mathrm{m}/\mathrm{s} \end{gathered}$$

Hence, the initial velocity of the car is 25 m/s.