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16/09/2020 6:15 pm
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Train A and train B are running on parallel tracks in the opposite directions with speed of 36 km/hour and 72 km/hour, respectively. A person is walking in train A in the direction opposite to its motion with a speed of 1.8 km/hour. Speed (in ms–1) of this person as observed from train B will be close to : (take the distance between the tracks as negligible)
(1) 30.5 ms–1
(2) 29.5 ms–1
(3) 31.5 ms–1
(4) 28.5 ms–1
1 Answer
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16/09/2020 6:19 pm
Correct answer: (2) 29.5 ms–1
Explanation:
VA = 36 km/hr = 10 m/s
VB = –72 km/hr = –20 m/s
Vman = – 1.8 km/hr = –0.5 m/s
Vman, B = Vman, A + VA,B
= Vman, A + VA – VB
= – 0.5 + 10 – (–20)
= – 0.5 + 30
= 29.5 m/s