A piece of stone tied to a string is made to revolve in a circular orbit of radius r with other end of the string as the centre. If the string breaks, the stone will:

When a stone is whirled in a circular orbit, its instantaneous velocity at any point is always directed along the tangent to the circle at that point. To maintain this circular path, a centripetal force (provided by the tension in the string) must act continuously toward the center. According to Newton's first law of motion, an object will maintain its state of motion unless acted upon by an external force. When the string breaks, the centripetal force suddenly vanishes. Consequently, the stone no longer experiences the inward pull required to change its direction. Due to inertia, the stone continues to move in a straight line along the direction of its instantaneous velocity at the moment of release, which is the tangent to the circular path.