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A passenger sitting in a train A moving at 90 km/h observes another train B moving in the opposite direction for 8 s. If the velocity of the train B is 54 km/h, then length of train B is

Asked in JEE Main 13th April 2nd Shift 2023 · Relative velocity in one dimension

• (1) 80 m
• (2) 120 m
• (3) 320 m
• (4) 200 m

Step-by-step solution

Why the other options are wrong

• (1) Subtracts the speeds (36 km/h = 10 m/s) though the trains move in opposite directions.
• (2) Uses B's own speed, 15 m/s, instead of the relative speed.
• (4) Uses A's own speed, 25 m/s, instead of the relative speed.

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