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 :

Options

A. `(t_1)+t_2)/2`
B. (t_1t_2)/(t_2-t_1)`
C. (t_t_2)/(t_2+t_1)`
D. ` t_1 -t_2 `

Answer

B

Explanation

Velocity fo girl w.r.t. escalator, ` v_(ge) = d/t_1`
velocity of girl on moving escalator w.r.t. ground
` vec v_(fG) = vec v_(ge) + vec v(eG)`
i.e. ` v(gG)= v_(eG)` or ` d/t = d/t_1 + d/t_2`
` or ` 1/t = 1/t_1 + 1/t_2` or ` t= (t-1t_20/(t_1=t_2)`.