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 change in its velocity as it reaches a position, where the string is horizontal.

Options

A. `sqrt(u^(2)-2gL)`
B. `sqrt(2gL)`
C. `sqrt(u^(2)-gL)`
D. `sqrt(2(u^(2)-gL))`

Answer

D

Explanation

Using `K.E_(B) = P.E_(H)+K.E_(H)` find `v`
`vec(Delta V) = vec(v)-vec(u)=v hat(j)-u hat(i)` ,
`|Delta V| = sqrt(v^(2)+(-u)^(2))=sqrt(v^(2)+u^(2))`,