$A$ mass $M$ is suspended from a light spring. An additional mass $m$ added displaces the spring further by a distance $x$. Now the combined mass will oscillate on the spring with period:

• A
  $T = 2\pi \sqrt {\left( {mg/x(M + m)} \right)} $
• B
  $T = 2\pi \sqrt {\left( {(M + m)x/mg} \right)} $
• C
  $T = (\pi /2)\sqrt {\left( {mg/x(M + m)} \right)} $
• D
  $T = 2\pi \sqrt {\left( {(M + m)/mgx} \right)} $