Q140 / 180 · JIPMER 2018 · Physics

A runner starts from O and goes to O following path OQRO in lhr. What is net displacement and average speed? Figure

  • Correct answer
    A
    $0,3.57 \mathrm{~km} / \mathrm{hr}$
  • B
    $0,0 \mathrm{~km} / \mathrm{hr}$
  • C
    $0,2.57$ km/hr
  • D
    $0,1 \mathrm{~km} / \mathrm{hr}$

Solution

$\because$ Runner starts from O and goes to O . So, net displacement is zero. $\begin{aligned} \because \text { Average speed } & =\frac{\text { Total distance }}{\text { Total time }} \\ & =\frac{\mathrm{OQ}+\mathrm{QR}+\mathrm{RO}}{\text { total time }}\end{aligned}$ $\begin{aligned} & \frac{1 \mathrm{~km}+(2 \pi \mathrm{r})\left(\frac{1}{4}\right)+1 \mathrm{~km}}{1 \mathrm{hr}} \\ = & 2+\frac{\pi}{2}=3.57 \mathrm{~km} / \mathrm{hr}\end{aligned}$

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

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