Question

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

Answer 1

Time taken by the car to stop = 10 seconds

Let the initial velocity of the car = u

Final velocity = 0

Retardation = 2.5 m/s² or Acceleration = $-$2.5 m/s²

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

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

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