A stone of mass 1 ,kg is tied with a string and it is whirled in a vertical circle of radius 1 ,m .

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5.Work, Energy, Power and Collision

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A stone of mass $1 \,kg$ is tied with a string and it is whirled in a vertical circle of radius $1 \,m$. If tension at the highest point is $14 \,N$, then velocity at lowest point will be ............ $m / s$

A

$3$

B

$4$

C

$8$

D

$6$

Solution

(c)

$T+m g=\frac{m v^2}{R}$ (at the highest point)

$14=\frac{1\left(v^2\right)}{R(1)}+10$

$v^2=4 \quad \Rightarrow v=2 \,m / s$

Using mechanical energy conservation

$\frac{1}{2}(1) u^2=\frac{1}{2}(1)\left(2^2\right)+1(10)(2)$

$u^2=64 \quad \Rightarrow u=8 \,m / s$

Standard 11

Physics

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