A block of mass 3m is placed on a frictionless horizontal surface, and a second block of mass m is placed on top of the first block. The surfaces of the blocks are rough. A constant force of magnitude F is applied to the first block.
a) Identify the horizontal force that causes the block of mass m to accelerate.
b) Assume that the upper block does not slip on the lower block, and find the acceleration of each block in terms of m and F.