Q122 / 160 · AP EAMCET 2023 (16 May Shift 1) · Physics

A person walks up a stalled escalator in $80 \mathrm{sec}$. When standing on the same escalator, now moving, he is carried up in 20 s. The time taken by him to walk up the moving escalator is

  • A
    $4 \mathrm{~s}$
  • B
    $8 \mathrm{~s}$
  • C
    $12 \mathrm{~s}$
  • Correct answer
    D
    $16 \mathrm{~s}$

Solution

Let distance travelled $=\mathrm{D}$ Speed of a person walks up $v_1=\frac{D}{80}$ Speed of escalator $v_2=\frac{D}{20}$ Total speed $\mathrm{v}=\mathrm{v}_1+\mathrm{v}_2 20$ $\begin{aligned} & =\frac{D}{80}+\frac{D}{20} \\ & =\frac{D+4 D}{80}=\frac{5 D}{80}\end{aligned}$ The time taken by him $\mathrm{t}_0$ walk up the moving escalator is $\begin{aligned} & t=\frac{D}{5 D / 80} \\ & =16 \mathrm{~s}\end{aligned}$

Hence, the correct answer is option: 'D'.

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