Look at the diagram. Since we are on a frictionless incline, the only force acting on the blue object along the incline is the component of the force of gravity ( ) parallel to it, i.e. ).
So, the net force acting on the object along the incline is given by:
But what do we know about ? Newton's second law!
Do you have any experience solving these sorts of problems?
You can do the experiments at this website:
CalcTool: Object on a slope calculator
Give M different values and see what happens to the acceleration.