Solving Accelerated Block Problem with Friction & Angle Alpha

[Kruger]

A block is accelerated with a, take a look at the picture. There is a friction between the red block and the other one with mass m1. The friction is given by the coefficient u1.

I have to determine a such that the blue block is not moving relative to the red one. a has to bi in depenence of angle alpha.

Homework Equations

The relevant equations are basically Newton's equations.

The Attempt at a Solution

What I have done so far is the following: One force acting on the block is coming from the gravitational field, so F_g=m1*g. I have splitted this one in components: F||=sin(alpha)*F_g and (already added friction) F_s=cos(alpha)*F_g*(1-u1).

I don't know how I can go on. The basic problem is I don't really know how a acts one the block. And how I've to balance the forces.

 

[OlderDan]

There will be a range of accelerations that will prevent the block from slipping because friction can act either up the plane or down the plane. Are you supposed to be finding the minimum accleration, maximum acceleration, or both?

You know the blue block must have the same acceleration as the red ramp. Draw all of the forces acting on the block. The sum of all the forces must be horizontal and have magnitude ma.