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Question

# A stone of mass 1 kg is tied of the end of a string 1 m long. It is whirled in a vertical circle. If the velocity of stone at the top is 4 m/s. What is the tension in the string at the lowest point? Take g=10 m/s2

A
6 N
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B
66 N
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C
5.2 N
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D
76 N
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Solution

## The correct option is B 66 NLet the velocity at lowest point is v and at highest point be u, then according to law of conservation of energy. energy at lowest point= energy at highest point.⇒12mv2=mg(2r)+12mu2⇒v=√u2+4rg=√42+(4×1×10)=√56At lowest point, mv2r=T−mg⇒T=mg+mv2r=mg+m(√56)2r (r=1)⇒T=mg+56 m=66×m=66×1=66 N.

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