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 [IIT 1998; CBSE PMT 2004]

• A.             \[\sqrt{{{u}^{2}}-2gL}\]
• B.               \[\sqrt{2gL}\]
• C.             \[\sqrt{{{u}^{2}}-gl}\]
• D.               \[\sqrt{2({{u}^{2}}-gL)}\]