A block of mass $m$ rests on a frictionless wedge of angle $\theta$ as in the figure. The wedge is given an acceleration $a$. What is the minimum value of $a$ so that the mass $m$ falls freely?
I have solved a similar problem, where the acceleration was in the opposite direction as in this question, and the condition was to prevent the block from sliding down. The accleration in that question came to be equal to $(g\;tan\theta)$. What exactly must be done here so that the block falls freely? I don't need an actual answer. Just how are we to find it.