A body of mass 1, kg is thrown upwards with a velocity 20, m/s . It momentarily comes to rest after

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5.Work, Energy, Power and Collision

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A body of mass $1\, kg$ is thrown upwards with a velocity $20\, m/s$. It momentarily comes to rest after attaining a height of $18\, m$. How much energy is lost due to air friction ............. $\mathrm{J}$ $(g = 10\, m/s^2)$

A

$30$

B

$40$

C

$10$

D

$20$

Solution

$\mathrm{KF}_{\text {initial}}=\frac{1}{2} \mathrm{mu}^{2}=200 \mathrm{J}$

$(\mathrm{mgh})_{\max }=200 \mathrm{J}$

$\mathrm{h}=20 \mathrm{m}$

The height travelled by the body ( $\left.h^{\prime}\right)=18 \mathrm{m}$

loss of energy $=\mathrm{mgh}-\mathrm{mgh}^{\prime}=20 \mathrm{J}$

Standard 11

Physics

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