Aball is thrown vertically down with velocity of 5m/s . With what velocity should another ball be th

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2.Motion in Straight Line

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Aball is thrown vertically down with velocity of $5m/s$. With what velocity should another ball be thrown down after $2$ seconds so that it can hit the $1^{st}$ ball in $2$ seconds.........$m/s$

A

$40$

B

$55 $

C

$15 $

D

$25$

Solution

For ball $1$

$u=5 \mathrm{m} / \mathrm{s}$

$t=4 \mathrm{secs}$

For ball $2$

$u=u \mathrm{m} / \mathrm{s}$

$t=2 \mathrm{secs}$

For collision equating heights $h=u t+\frac{1}{2} g t^{2}$

$5 \times 4+\frac{1}{2} 10 \times 4^{2}=u \times 2+\frac{1}{2} 10 \times 2^{2}$

$\mathrm{u}=40 \mathrm{m} / \mathrm{s}$

Standard 11

Physics

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