A point object `O` can move along vertical line `AB` as shown in figure . When image of the object is first visible to `D` then it is released at t=0 from rest from `A` . The time for which image is visible to `D` is :

Options

A. `sqrt((6L)/(g))`
B. `sqrt((2L)/(g))`
C. `sqrt((3L)/(g))`
D. `t rarr oo`

Answer

A

Explanation

Required time is given by `3L= (1)/(2)gt^(2) implies t=sqrt((6L)/(g))`
`(A)`