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  • A person wacks up a stalled escalator in . Wh

A person wacks up a stalled escalator in \mathrm{ 90 \, \mathrm{sec}}. When standing on the same escalator, now moving, he is carried in \mathrm{60\, \mathrm{sec}}. The time it would take him to walk up the moving escalator will be-

Option: 1

27 sec.


Option: 2

72 sec.


Option: 3

18 sec.


Option: 4

36 sec.


Answers (1)

best_answer

If u and v are the speeds of the person and of the escalator, then.

          \mathrm{\frac{l}{u}=90 \quad, \quad \therefore \quad u=\frac{l}{90} \quad\left\{\begin{array}{l} \because \text { spued } \\ =\frac{\text { dirtance }}{\text { tima. }} \end{array}\right.}

and     \mathrm{\frac{l}{v}=60 \quad, \quad \therefore v=\frac{l}{60}}

If  t is the required time, then 

\mathrm{\begin{aligned} & t=\frac{l}{u+v}=\frac{l}{\frac{l}{90}+\frac{l}{60}} \\ & t=\frac{l}{\frac{l}{30}\left[\frac{1}{3}+\frac{1}{2}\right]}=\frac{30}{\frac{1}{3}+\frac{1}{2}} \\ & t=\frac{180}{5}=36 \end{aligned}}

\mathrm{t=36 \, \mathrm{sec} \text { Ans. }}

Posted by

Devendra Khairwa

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