Physics problem with an inclined plane that accelerating..help?

Consider A and B as a whole object. Total mass = M + m where M=mass of wedge, and m= mass of object on inclined plane. The whole system (A+B) is subject to two forces, one from the external force F acted along -ve x direction, and a force from the rail acting +ve y direction. The rail force is variable in magnitude so that A (wedge) is always held at the line y=0. The forces between the wedge and the object are internal forces which are equal and opposite to each other (and normal to the slope); so they won't affect the overall acceleration. As a result, the overall acceleration is parallel to external force F and its magnitude is:

A = F / (M + m)

The above eqn is true as long as M+m > 0.

Let a be the accel of B. The direction of a must be normal (i.e. pointing to the N-W direction) to the incline plane, since the normal reaction from the slope is the only force acting on B.

Now consider the resolution of acceleration. The real accel of B is "a" normal to the plane; the component of accel parallel to F is a*sin(theta), which equals to A from our previous calculation. So

a*sin(theta) = A
a = A / sin(theta) (assume theta <> 0) (*)
= F / [(M+m) * sin(theta)]

So a->infinity as theta->0!

But when theta=0, then step (*) is illegal (we cannot divide both side by ZERO). If theta=0, your question does not make sense. Because the normal force is parallel to +ve y-axis, it won't accel B parallel to x-axis. The wedge (which is a sheet at this case) will slide under the object. The object remains stationary and drops off from the right end of the wedge.

look on your figures, as a mass is retarding the action + acceleration is on a prone plane=>acceleration must be constantly below g i.e. 9.8 m/s^2. How a acceleration of 12 m/s^2 achieveable?