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Laws Of Motion

Question
CBSEENPH11017013

A body of mass m is tied with string and rotated in vertical circle of radius r. The body is given the velocity u at lowest point space space left parenthesis u greater than square root of 5 g r right parenthesis end root.  What is the tension at the highest point and does the difference in the tensions at the lowest and the highest point depend upon u?

Solution


Tension in the string at any point is given by,
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                equals m over r left parenthesis u squared minus 2 g r plus 3 r g cosθ right parenthesis
 At highest point,  straight theta equals 180 degree

Therefore, 

T subscript H equals m over r left parenthesis u squared minus 2 g r minus 3 r g right parenthesis space equals space m over r left parenthesis u squared minus 5 g r right parenthesis
At the lowest point, straight theta equals 0 degree
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∴               T subscript L minus T subscript H equals 6 m g
The difference in the tension at the highest and the lowest point does not depend upon velocity at the lowest point and is constant, equal to 6 mg.