Consider the following figure, where a mass $m$ is placed on a wedge which is accelerated to the right ($\vec a$) which could be negative. The coefficient of friction between the mass and the wedge is $\mu$.
I sketched the 3 forces I know that the mass "feels" but I don't know that happens when the wedge is accelerated. Could any one give me a hint for this?
Is this $m\vec a$ vector I sketched in red correct?