Preeti reached the metro station and found that the escalator was not working. She walked up the stationary escalator in time `t_1`. On other days, if the remains stationary on the moving escalator, then the escalator takes her up in time `t_2`. The time taken by her to walk up on the moving escalator will be :A. `(t_1 t_2)/(t_2 - t_1)`B. `(t_1 t_2)/(t_2 + t_1)`C. `t_1 - t_2`D. `(t_1 + t_2)/(2)`

Preeti reached the metro station and found that the escalator was not

1.	Preeti reached the metro station and found that the escalator was not working. She walked up the stationary escalator in time `t_1`. On other days, if the remains stationary on the moving escalator, then the escalator takes her up in time `t_2`. The time taken by her to walk up on the moving escalator will be :A. `(t_1 t_2)/(t_2 - t_1)`B. `(t_1 t_2)/(t_2 + t_1)`C. `t_1 - t_2`D. `(t_1 + t_2)/(2)`
Answer» Correct Answer - B Velocity of Preeti w.r.t. elevator `= (l)/(t_1)` Velocity of elevator w.r.t. ground `= (l)/(t_2)` Then velocity of girl w.r.t. ground `vec v_("preeti") = vecv_("preeti,elevator") + vecv_("elevator")` `(l)/(t) = (l)/(t_1) + (l)/(t_2)` `rArr t = (l)/(l/(t_1) +(l)/(t_2)) =(t_1 t_2)/(t_1 + t_2)`.

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