Question

An up escalator is going at the rate of 10 step/min. How many steps should I move down on it as to look like that I am at rest to a person standing on ground.

• A. 0 steps
• B. 20 steps
• C. 10 steps
• D. 5 steps

Answer 1

The correct option is C

10 steps

So in the same time you have to come down by 10 steps so as to remain at the $5^{th}$ step. So technically after a minute also your displacement is 0. Hence your velocity = 0, w.r.t. a person on ground.
Also, mathematically

= Velocity of lift w.r.t to ground = 10 steps/min
= $V_{man}$ with respect to ground = 0 as the man's position shouldn't change in time.
Now question asks how much should you move down on a moving lift?
= Velocity of man w.r.t. lift
= $v_m-v_l$
= 0 - 10
= - 10 steps/min
This means man should come down 10 steps per minute on the moving lift.