String of a pendulum of length l is displaced through 90^o from vertical and released. Then, minimum

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5.Work, Energy, Power and Collision

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The string of a pendulum of length $l$ is displaced through $90^o$ from the vertical and released. Then, the minimum strength of the string in order to withstand the tension as the pendulum passes through the mean position is

A

$mg$

B

$3\,mg$

C

$5\,mg$

D

$6\,mg$

Solution

$\mathrm{T}-\mathrm{mg}=\frac{\mathrm{mv}^{2}}{\mathrm{R}}$

$\mathrm{T}-\mathrm{mg}=\frac{\mathrm{m} \times(\sqrt{2 \mathrm{gR}})^{2}}{\mathrm{R}}$

$\mathrm{T}-\mathrm{mg}=\frac{2 \mathrm{mg} \mathrm{R}}{\mathrm{R}}$

$\mathrm{T}=3 \mathrm{mg}$

Standard 11

Physics

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(JEE MAIN-2016)