what is the speed with which a stone leaves a string if it is let go when the length of the string holding the stone is 0.7m and is revolving at 3 revolutions pre second

Radius of the circular path of the string is, r = 0.7 m

Speed of revolution = 3 revolution per sec = 3 × 2π × r m/s

=> v = 3 × 2π × 0.7 = 13.2 m/s

This is the speed with which the stone is revolving in the circular path. This is also the tangential velocity of the stone at any instant of its motion. Therefore, when the string breaks it will fly off at speed 13.2 m/s.