A mass m is suspended by means of two coiled spring which have the same length in unstretched condition as in figure. Their force constant are k₁ and k₂ respectively. When set into vertical vibrations, the period will be

• A

  $2\pi \sqrt{\left(\frac{m}{k_1{k}_2}\right)}$

• B

  $2\mathrm{\pi }\sqrt{\mathrm{m}\left(\frac{{\mathrm{k}}_1}{{\mathrm{k}}_2}\right)}$

• C

  $2\mathrm{\pi }\sqrt{\left(\frac{\mathrm{m}}{{\mathrm{k}}_1-{\mathrm{k}}_2}\right)}$

• D

  $2\mathrm{\pi }\sqrt{\left(\frac{\mathrm{m}}{{\mathrm{k}}_1+{\mathrm{k}}_2}\right)}$