A person goes from point P to point Q covergin 1 / 3 of the distance with speed 10 ~km / hr , the next 1 / 3 of the distance at 20 ~km / hr and the last 1 / 3 of the distance at 60 ~km / hr . The average speed of the person is

Correct answer: (C) 18 ~km / hr. V_avg =(Total Distance)/(total time)=S/((S / 3)/10+(S / 3)/20+(S / 3)/60) ~V_avg =18 ~km / hr

Q40 / 54 · KVPY 2017 (5 Nov SA) · Physics

A person goes from point $\mathrm{P}$ to point $\mathrm{Q}$ covergin $1 / 3$ of the distance with speed $10 \mathrm{~km} / \mathrm{hr}$, the next $1 / 3$ of the distance at $20 \mathrm{~km} / \mathrm{hr}$ and the last $1 / 3$ of the distance at $60 \mathrm{~km} / \mathrm{hr}$. The average speed of the person is

A
$30 \mathrm{~km} / \mathrm{hr}$
B
$24 \mathrm{~km} / \mathrm{hr}$
Correct answer
C
$18 \mathrm{~km} / \mathrm{hr}$
D
$12 \mathrm{~km} / \mathrm{hr}$

Solution

$V_{\text {avg }}=\frac{\text { Total Distance }}{\text { total time }}=\frac{\mathrm{S}}{\frac{\mathrm{S} / 3}{10}+\frac{\mathrm{S} / 3}{20}+\frac{\mathrm{S} / 3}{60}}$ $\mathrm{~V}_{\text {avg }}=18 \mathrm{~km} / \mathrm{hr}$

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

Solution

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