For what value of 'a'the block falls freely?

Explanation

In the time the wedge moves a distance x towards left with acceleration a the block falls through a height h with acceleration g `(x=(1)/(2)at^(2))/(h=(1)/(2)g t^(2))rArr (x)/(h)=(a)/(g)`
`rArr cot theta = (a)/(g) " " a = g cot theta`