Question

A man sees a train passing a bridge 1 km long. The length of the train is half that of the bridge. If the train clears the bridge in 2 minutes, find the speed of the train in km/hr. [4 MARKS]

Answer 1

Concept: 1 Mark
Application: 3 Marks

According to the given condition

The total distance that needs to be covered by the train to cross the bridge

$=\frac{1}{2}+1$

$=\frac{1+2}{2}$

$=\frac{3}{2}km$

Given that the time taken = 2 minutes when converting into hour we have $\frac{2}{60}=\frac{1}{30}hr$

If the distance covered by the train = x km

we have

$\begin{array}{cc}\text{Distance Covered}& \text{Time Taken}\\ \frac{3}{2}\text{km}& \frac{1}{30}\text{hr}\\ x\text{km}& 1\text{hr}\end{array}$

Cross multiplying we have

$\frac{3}{2}\times 1=x\times \frac{1}{30}$

$\frac{3}{2}=\frac{x}{30}$

45 = x

Hence the speed of the train = 45 km/hr