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) √2gL (c) √u² - gl (d) √2 (u² - gL)

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) √2gL (c) √u² - gl (d) √2 (u² - gL)