Question

Calculate the acceleration of a bus which is moving at $40{km}/{h}\;$
and stops after 5s of applying the brakes.

Answer 1

Hint : In this question we have to find the acceleration of the bus. So we must know what acceleration is. That is, acceleration is defined as the rate of change of velocity with the change in time. Thus by using the equations of motion we can calculate the acceleration.

Complete step-by-step solution:
Given that,
The initial velocity is zero. That is,
$u=0{m}/{s}\;$
Also given,
$\begin{aligned} & V=40{km}/{h}\; \\\ & t=5s \\\ \end{aligned}$
Converting the velocity in kilometer hour to metre per second we get,
$V=40\times \dfrac{1000}{3600}$
$V=40\times \dfrac{5}{18}$
$\therefore V=11.11{m}/{s}\;$
Then acceleration of the bus can be calculated using the equation of motion,
$V=u+at$
Then by substituting the values we get,
$V=0+a\times 5$
$\Rightarrow V=5a$
$a=\dfrac{V}{5}$
$a=\dfrac{11.11}{5}$
$\therefore a=2.22{m}/{{{s}^{2}}}\;$
Thus the acceleration of a bus which is moving at $40{km}/{h}\;$ and stops after 5s of applying the brakes is 2.22 metre per second square.

Note: If the net external force acting on the body is zero then the acceleration of the body also becomes zero. That is, in this case the body is either in the state of rest or uniform motion. Here the velocity remains constant during the entire motion. Thus acceleration becomes zero.