A ball is thrown upwards. It takes 4,sec to reach back to ground. Its initial velocity is........ ms

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2.Motion in Straight Line

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A ball is thrown upwards. It takes $4\,sec$ to reach back to the ground. Its initial velocity is........$ms^{-1}$

A

$30$

B

$10$

C

$40$

D

$20$

Solution

time for one side $t=\frac{4}{2}=2 s$

$0=u-g t \Rightarrow u=g t=10 \times 2=20 \mathrm{m} / \mathrm{s}$

$\mathbf{o r}$

time of flight $T=\frac{2 u}{g} \Rightarrow u=\frac{g T}{2}=\frac{10 \times 4}{2}=20 m / s$

Standard 11

Physics

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