151. Preeti reached the metro station and found that theescalator was not working. She walked up thestationary escalator in time t₁. On other days, if sheremains stationary on the moving escalator, then theescalator takes her up in time t₂. The time taken byher to walk up on the moving escalator will be
(1) (t₁ + t₂)/2 (2) t₁t₂/(t₂ - t₁)
(3) t₁t₂/(t₂ + t₁) (4) (t₁ - t₂)
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Thus the time taken by her to walk up on the moving escalator will be
t' = t1 t2 / t1 + t2
Option (3) is correct.
Explanation:
t1 = time at stationary
t2 = time by escalator
d displacement of escalator
v1 = Velocity of stationary
v2 = Velocity of Preeti
( V1 + V2 ) = d / t'
V1 = d / t1
V2 = d / t2
d / t1 + d / t2 = d / t'
t' = t1 t2 / t1 + t2
Thus the time taken by her to walk up on the moving escalator will be
t' = t1 t2 / t1 + t2
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