Question

A ball on a string moves around a complete circle, once a second, on a frictionless, horizontal table. The tension in the string is measured to be 6.0N . What would the tension be if the ball went around in only half a second?

Answer 1

The tension in the string balances out, and thus equals the centripetal force of the ball 

T = mv^2/r 

if it only takes half the time to finish one orbit it has to be moving at twice the original speed. 

And since v is squared T will increase by 4 

T' = m(2v)^2/r 

T' = 4mv^/r = 4T 

T' = 24.0 N

I hope my answer has come to your help. Have a nice day ahead and may God bless you always!