A mass m is revolving in a vertical circle at the end of a string of length 20 cm. By how much does the tension of the string at the lowest point exceed the tension at the top most point?

The tension T1 at the topmost point is given byT1=mv1220−mgCentrifugal force acting outward while weight acting downward.The tension T2 at the lowest pointT2=mv2220+mgcentrifugal force and weight (both) acting downwardT2−T1=mv22−mv1220+2mgv12=v22−2gh or  v22−v12=2g(40)=80g∴ T2−T1=80mg20+2mg=6mg