Question

Two trains , each 180 m long , are moving towards each other on parallel tracks at speeds of 50 km/hr and 70 km/hr. In how many seconds will they completely cross each other ?

• A. 10.4
• B. 10.8
• C. 10.2
• D. 10.6

Answer 1

Answer:

B. 10.8

Since the trains are moving towards each other, their relative speed is the sum of their speeds.

Relative speed

$50 + 70 = 120 \text{ km/h}$

Convert to m/s:
$120 \times \frac{1000}{3600} = 33.33 \text{ m/s}$

Total distance to be covered

$180 + 180 = 360 \text{ m}$

Time taken

$\text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{360}{33.33}$
$\text{Time} = 10.8 \text{ seconds}$

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The trains will completely cross each other in 10.8 seconds