A stone is tied to a string of length l and is whirled in a vertical circle with the other end of the string as 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 velocity as it reaches a position where the string is horizontal (g being acceleration due to gravity) is

Options

A. `sqrt(u^(2) - 2gL)`
B. `sqrt2gL`
C. `sqrt(u^(2) - gL)`
D. `sqrt(2(u^(2) - gL)`

Answer

`(4)`

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))`