Two trains, each $50 ext{ m}$ long, are travelling in the opposite direction with velocities $10 ext{ m/s}

Question

Two trains, each $50 	ext{ m}$ long, are travelling in the opposite direction with velocities $10 	ext{ m/s}$ and $15 	ext{ m/s}$. The time of crossing is:

Accepted Answer

1.  **Concept - Relative Velocity:** When two objects move in opposite directions, their relative velocity is the sum of their individual speeds. 
    *   $v_{relative} = v_1 + v_2 = 10 + 15 = 25 	ext{ m/s}$ .
2.  **Total Distance:** To cross each other completely, the total distance covered is the sum of the lengths of both trains.
    *   $d = L_1 + L_2 = 50 + 50 = 100 	ext{ m}$.
3.  **Calculate Time:** Time taken to cross is given by distance divided by relative speed.
    *   $t = \frac{d}{v_{relative}} = \frac{100}{25} = 4 	ext{ sec}$.

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