A person walks up a stalled 15 m long escalator in 90 s. When standing on the same escalator, now moving, the person is carried up in 60 s. How much time would it take that person to walk up the moving escalator? Does the answer depend on the length of the escalator?

Answer

C

Explanation

`v_1`=speed of persion
`v_2`=speed pf escalator
`v_1=l/(t_1)` and `v_2=l/(t_2)`
`:. t=l/(v_1+v_2)=l/((l/t_1)+(l/t_2))`
`=(t_1t_2)/(t_1+t_2)=(90xx60)/(90+60)=36s`