A bus travelling first one-third distance at a speed of 10 km/h , next one-third at 20 km/h and at l

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2.Motion in Straight Line

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A bus travelling the first one-third distance at a speed of $10\; km/h$, the next one-third at $20\; km/h$ and at last one-third at $60\; km/h$. The average speed of the bus is ........ $km/h$

A

$18$

B

$9$

C

$16$

D

$48$

Solution

$v_{a v g}=\frac{3 v_{1} v_{2} v_{3}}{v_{1} v_{2}+v_{2} v_{3}+v_{3} v_{1}}$

$v_{a v g}=\frac{3 \times 10 \times 20 \times 60}{10 \times 20+20 \times 60+60 \times 10}$

$v_{a v g}=18 \;kmh ^{-1}$

Standard 11

Physics

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