Question

A 240 m long train crosses a man walking at a speed of 4.5 km/h in the opposite direction in 12 seconds. What is the speed (in km/h) of the train?

• A. 61.5
• B. 67.5
• C. 60.5
• D. 58.5

Answer 1

Answer:

B. 67.5

Train length = 240 m
Time = 12 s
Man speed = 4.5 km/h (opposite direction)

Convert man’s speed to m/s

$4.5 \times \frac{5}{18} = 1.25 \text{ m/s}$

Relative speed (opposite direction)

Let train speed = (v) m/s

$\text{Relative speed} = v + 1.25$

Use distance = speed × time

$240 = (v + 1.25)\times 12$
$v + 1.25 = 20$
$v = 18.75 \text{ m/s}$

Convert to km/h

$18.75 \times \frac{18}{5} = 67.5$

Final Answer: 67.5 km/h