An elastic spring, suspended vertically gets extended in length by i, when a mass M is attached at other end. What will be the period of vibration of the spring when a mass m is attached at the lower end ?

• A

  $2\mathrm{\pi }\sqrt{\left(\frac{\mathrm{l}}{\mathrm{g}}\right)}$

• B

  $2\mathrm{\pi }\sqrt{\left(\frac{\mathrm{Ml}}{\mathrm{mg}}\right)}$

• C

  $2\mathrm{\pi }\sqrt{(\mathrm{Mg}/\mathrm{ml})}$

• D

  $2\mathrm{\pi }\sqrt{(\mathrm{ml}/\mathrm{Mg})}$