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physics problem

a person walks up a stalled escalator in 90 sec.W HEN STANDING ON THE SAME ESCALATOR,NOW MOVING,HE IS CARRIED IN 60 SEC.THE TIME HE WOULD TAKE TO WALK UP THE MOVING ESCALATOR? A)27S B) 72S C)18S D) 36S E)48S

Note by Sonali Sukesh
4 years, 9 months ago

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D

- 4 years, 9 months ago

thank u very much .........but i would like to know the steps too...... how did u do it?

- 4 years, 9 months ago

Assume that the length of the escalator is $$1$$ ,the speed at which the person walks is $$\frac{1} {90}$$ and the speed of the escalator is $$\frac{1} {60}$$.So,the speed at which he moves up the moving escalator is $$\frac{1} {90} +\frac{1} {60} =\frac{5} {180}=\frac{1} {36}$$.So,it takes 36 seconds for him to walk up the moving escalator.

- 4 years, 9 months ago