Chapter 4, Problem 55P

(III) A small block of mass m rests on the sloping side of a triangular block of mass M which itself rests on a horizontal table as shown in Fig. 4–47. Assuming all surfaces are frictionless, determine the magnitude of the force $\stackrel{\to }{F}$ that must be applied to M so that m remains in a fixed position relative to M (that is, m doesn’t move on the incline). [Hint. Take x and y axes horizontal and vertical.]