Two masses m1 and m2 are suspended together by a massless spring of constant K. When the masses are in equilibrium, m1 is removed without disturbing the system. The amplitude of oscillations is

With mass m2 alone, the extension of the spring l is given as m2g=kl                ...(i) With mass (m1+m2), the extension  l' is given by  (m1+m2)g=k(l+Δl)           ....(ii) The increase in extension is Δl which is the amplitude of vibration. Subtracting (i) from (ii), we get m1g=kΔl  or  Δl=m1gk