Question

A certain length bus moving at a speed of 40kmph crosses a man running at a speed of 5kmph in opposite direction in 4/5 seconds. Same bus can cross certain length bridge in 18 seconds. Find the time taken by man to cross same bridge.
1. 128 seconds
2. 120 seconds
3. 123 seconds
4. 133 seconds
5. 137 seconds

Answer 1

Correct Answer - Option 5 : 137 seconds

Given:

⇒ Speed of bus = 40kmph = 40 × 5/18 = 100/9 m/s

⇒ Speed of running man = 5kmph = 5 × 5/18 = 25/18 m/s

Let length of bus be a m.

Relative speed = 100/9 + 25/18 = 225/18 m/s

Then,

⇒ 4/5 = a/(225/18)

⇒ a = 10 m

Let length of bridge be b m.

⇒ (10 + b)/(100/9) = 18

⇒ b = 190m

∴ Time taken by man to cross same bridge = 190/(25/18) = 136.8 ≈ 137 seconds