Question

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)

Answer 1

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