A block of mass m is connected to another block of mass M by a spring (massless) of spring constant k. The blocks are kept on a smooth horizontal plane. Initially the blocks are at rest and the spring is unstretched. 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.

Question

( A ) $\frac{mF}{(m+M)}$
( B ) $\frac{(m+M)F}{mF}$
( C ) $\frac{mF}{M}$
( D ) $\frac{MF}{(m+M)}$