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Question

# A mass m is revolving in a vertical circle at the end of a string of length 20 cms. By how much does the tension of the string at the lowest point exceed the tension at the topmost point

A
6mg
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B
2mg
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C
mg
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D
4mg
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Solution

## The correct option is A 6mgAs per the question, the situation can be represented as We have the force equation as TLower=mg+mu2r TUpper=mv2r−mg So we have TLower−TUpper=mr(u2−v2)+2mg...(1) Also, we have u2−v2=[(√5rg)2−(√rg)2]=4rg...(2) Putting value of (2) in (1) we have TLower−TUpper=mr×4rg+2mg=6mg

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