Question

Two trains cross each other at a speed of 70 kmph and 50 kmph, respectively. If the total length of both the trains is 1500m, find the time in which they will cross each other. The trains were moving in the opposite direction.

• A. 43 seconds
• B. 41 seconds
• C. 45 seconds
• D. 42 seconds

Hint:

Always convert kmph to m/s by multiplying with \(5/18\) when the distance is in meters and the time is in seconds.

Answer 1

The Correct Option is C

Concept: When two objects move in opposite directions, their Relative Speed is the sum of their individual speeds. \[ \text{Time} = \frac{\text{Total Distance (Sum of lengths)}}{\text{Relative Speed}} \]
Step 1: Calculate Relative Speed in m/s.
Relative Speed = \(70 + 50 = 120 \text{ kmph}\).
Convert to m/s: \(120 \times \frac{5}{18} = \frac{600}{18} = \frac{100}{3} \text{ m/s}\).

Step 2: Calculate the crossing time.
Total length = 1500 m. \[ \text{Time} = \frac{1500}{100/3} = 15 \times 3 = 45 \text{ seconds}. \]