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 lowest position and has a speed `u` . Find the magnitude of the cgange in its velocity as it reaches a position, where the string is horizontal.

Answer

B

Explanation

`-mgl = 1/2 mv^(2)-1/2 "mu"^(2)`
`v = sqrt(u^(2)-2gl)`
`|vec(Deltav)|=sqrt(v^(2)+u^(2)-2gl)`