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

Answer

A

Explanation

h=l
`tan^(-1)((v^2)/(Rg))`
`=tan^(-1)((400)/(100xx10))=tan^(-1)(2/5)`
`Deltav|=|v_f=v_i|="subtraction of"vectorsat 90^@`
`=sqrt(v^2+u^2-2vu.cos90^@)`
`=sqrt(v^2+u^2)`
`sqrt((u^2-2gl)+u^2)=sqrt(2(u^2-gl))`