Q7: A stone tied to a string of length L is whirled in a vertical circle with the other end of the string at the centre. At a certain instant of time, the stone is at its lowest position, and has a speed u. The magnitude of the change in its velocity as it reaches a position where the string is horizontal is
(a) u2−2gL
(b) u2−gL
(c) 2(u2−gL)
(d) 2gL