On a particle moving on a circular path with constant speed `v`, light is thrown from a projectors placed at the centre of the circular path. The shadow of the particle is formed on the wall. The velocity of shadow up the wall is

Options

A. `vsec^(2)varphi`
B. `v cos^(2)varphi`
C. `v cos varphi`
D. None of these

Answer

A

Explanation

`y=R tan theta`
`(dy)/(dt)=Rsec^(2)theta=(dv)/(dt), V_(y)=Rsec^(2)theta(omega)`
`V_(y)=Rsec^(2) theta(v/R)=Vsec^(2)theta`