JEE Main · 2023 · 13 Apr 2023 · Shift 2 · Kinematics

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 :

(A)80 m
(B)200 m
(C)120 m
(D)320 m✓ Correct

Answer: (D)

Solution

Convert velocities:

v_{A} = 90 \times \frac{5}{18} = 25

m/s,

v_{B} = 54 \times \frac{5}{18} = 15

m/s. Since the trains move in opposite directions, relative velocity

v_{r e l} = 25 + 15 = 40

m/s. The time taken for train B to pass the observer is 8 s, so length

L = v_{r e l} \times t = 40 \times 8 = 320

JEE Main · 2023 · 13 Apr 2023 · Shift 2 · Single correct option

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