JEE MAIN - Physics (2020 - 2nd September Morning Slot - No. 8)
Train A and train B are running on parallel
tracks in the opposite directions with speeds 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)
(take the distance between the tracks as negligible)
30.5 ms–1
29.5 ms–1
31.5 ms–1
28.5 ms–1
Explanation
Velocity of man with respect to ground
$${\overrightarrow V _{m/g}}$$ = $${\overrightarrow V _{m/A}}$$ + $${\overrightarrow V _{A}}$$
= -1.8 + 36
Velocity of man w.r.t. B
$${\overrightarrow V _{m/B}}$$ = $${\overrightarrow V _{m}}$$ - $${\overrightarrow V _{B}}$$
= –1.8 + 36 – (–72)
= 106.2 km/hr
= 29.5 m/s
$${\overrightarrow V _{m/g}}$$ = $${\overrightarrow V _{m/A}}$$ + $${\overrightarrow V _{A}}$$
= -1.8 + 36
Velocity of man w.r.t. B
$${\overrightarrow V _{m/B}}$$ = $${\overrightarrow V _{m}}$$ - $${\overrightarrow V _{B}}$$
= –1.8 + 36 – (–72)
= 106.2 km/hr
= 29.5 m/s
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