A mass m is revolving in a vertical circle


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a mass M is revolving in a vertical circle at the end of a string of length 20 CM by how much year does the tension of the string at the lowest point exceed the tension at the top most point.

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Let tension T_1 at the topmost point is given by,
T_1+mg=\frac{mv_1^2}{l}.....(1)
here tension and weight of body acting towards centre of circle and balancing centrifugal force acting outward. here l is length of string.

similarly, The tension T_2 at the lowest point is given by,
T_2-mg=\frac{mv_2^2}{l} .....(2)
here, tension acting inward while balancing centrifugal force and weight of body acting outward.

T_2-T_2=\frac{mv_2^2}{l}+mg-\frac{mv_1^2}{l}+mg\\\\=\frac{m}{l}(v_2^2-v_1^2)+2mg

we know,from law of kinematics equation,
v_1^2=v_2^2-2g(2l)

T_2-T_1=\frac{m}{l}\{2g(2l)\}+2mg\\\\=6mg

hence, answer is 6mg


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