At a metro station, a girl walks up a stationary escalator in time t1. If she remains stationary on the escalator, then the escalator take her up in time t2. The time taken by her to walk up on the moving escalator will be a) (t1 + t2)/2 b) t1t2/(t2 – t1) c) t1t2/(t2 + t1) d) t1 – t2
Let speed of girl on stationary escalator =Vg=(V1) speed of only escalator =Ve=(V2) slant distance =d Now, time to go up when escalator is stop, tg=Vgd=(=t1) ⇒Vg=tgd time req. to go-up when girl stops & escalator moves, te=Ved(=t2) ⇒Ve=t2d Now, when both girl & escalator moves up,velocity of girl with respect ot ground =Vg+Ve Time taken, t=Vg+Ved =t1d+t2dd t=t2+t1t1t2
