Question

A driver applies brakes when he sees a child on the railway track, the speed of the train reduces from $54kmph$ to $18kmph$ in $5s$. What is the distance traveled by train during this interval of time?

• A. $52m$
• B. $50m$
• C. $25m$
• D. $80m$

Answer 1

Answer: (B)

$50m$

Initial speed

$u=54kmph$

$\Rightarrow u=54\times \frac{5}{18}$

$\Rightarrow u=15m{s}^{-1}$

Final speed

$v=18kmph$

$\Rightarrow v=18\times \frac{5}{18}$

$\Rightarrow v=5m{s}^{-1}$

Time $t=5s$

Using $v=u+at$

$\therefore$ $15=5+a\times 5$

$⟹a=-2m/s^2$

Using $2aS=v^2-u^2$

where $S$ is the distance travelled.

$\therefore$ $2\times (-2)S=5^2-{15}^2$

$\Rightarrow S=50m$