A block of mass m is held motionless on a frictionless plane of mass M and angle of inclination ? (see Fig.). The plane rests on a frictionless horizontal surface. The block is released. What is the horizontal acceleration of the plane? (This problem already showed up as Problem 2.2. If you haven't already done so, try solving it using F = ma. You will then have a greater appreciation for the Lagrangian method.)