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Question

# 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 the lowest point will be (Take value of g=10 m/s2)

A
3 m/s
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B
4 m/s
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C
6 m/s
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D
8 m/s
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Solution

## The correct option is D 8 m/sLet v be the velocity at the highest point and u at the lowest point of the vertical circular path. At the highest point, equation of dynamics, T+mg=mv2R ⇒14+10=v21 ⇒v2=24 Applying mechanical energy conservation between lowest and highest point, taking potential energy zero at lowest point.12mu2+0=12mv2+mg(2R) ⇒12×1×u2=12×1×24+1×10×2×1 ⇒u2=64 ⇒u=√64=8 m/s Why this question? It intends to test the application of Newton's second law, concept of circular dynamics and energy conservation in a single package.

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