A ball after falling from a height of 10, m strikes roof of a lift which is descending do

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5.Work, Energy, Power and Collision

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A ball after falling from a height of $10\, m$ strikes the roof of a lift which is descending down with a velocity of $1\, m/s$. The recoil velocity of the ball will be .............. $\mathrm{m}/ \mathrm{s}$

A

$8 $

B

$11$

C

$12$

D

$15$

Solution

Speed of ball jast before striking with lift is-

$\mathrm{u}_{1}=\sqrt{2 \mathrm{g}} \mathrm{h}=\sqrt{2 \times 9.8 \times 10}=14 \mathrm{m} / \mathrm{s}$

As $\mathrm{M}_{\mathrm{lift}}>>>\mathrm{M}_{\mathrm{ball}}$

velocity of ball after collision with lift is $:-$

$\mathrm{v}_{1}=-\mathrm{u}_{1}+2 \mathrm{u}_{2}=-(-14)+2(-1)=12 \mathrm{m} / \mathrm{s}$

Standard 11

Physics

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