A mass of 0.675 kg on a frictionless table is attached to a string which passes through a hole in the table at the centre. If the radius of the circle in which the mass rotates is 5 m when its speed is 10 m s-1, find the tension of the string. It is found that on drawing down the string by 0.2 m, the tension is increased 4.63 times. Calculate the work done by the string on the revolving mass during the reduction of the radius.