A simple pendulum of mass m is performing vertical circular motion with its velocity at the highest point being V=√2gl , where l is the length of the string. Find the tension in the string when it reaches the lowest point.
A
2 mg
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B
6 mg
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C
7 mg
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D
3 mg
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Solution
The correct option is C 7 mg
From WET, ki+u1+WNC=kf+uf(WNC=0) 12m(2gl)+mg(2l)=12mu2+0 ⇒u2=6gl Tension at the lowest point is T=mg+mu2l(mu2l:centrifugalforce) =mg+ml(6gl) =7mg