Particles of masses 2M, m and M are respectively at points A, Band C with . m is much-much smaller than M and, at time t = 0, they are all at rest as given in figure. At subsequent times before any collision takes place.
Force on B due to towards BA
Force on B due to
towards BC
As (BC) = 2AB
Hence, m will move towards BA (i.e., 2M)