Q. 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 she 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) $\frac{t_1 + t_2}{2}$
B) $\frac{t_1t_2}{t_2 - t_1}$
C) $\frac{t_1t_2}{t_2 + t_1}$
D) $t_1 - t_2$
Explanation
[Solution] Speeds add: $L/t = L/t_1 + L/t_2$, so $t = \frac{t_1t_2}{t_1 + t_2}$. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.