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 [CPMT 1989, 1998 ; UPSEAT 2000]

• 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. \[T=2\pi \sqrt{\left( (M+m)/mgx \right)}\]