A block of mass m is connected to another block of mass M by a string (massless). The blocks are kept on a smooth horizontal plane. Initially the blocks are at rest. Then a constant force F starts acting on the block of mass M to pull it. Find the force on the block of mass m
(1) mF/m
(2) (M + m)F/m
(3) mF/(m + M)
(4) MF/(m + M)