A mass m is suspended by means of two coiled springs which have the same length in unstretched condition fig.  Their force constants are k₁ and k₂
 

k₁ and k₂  respectively. When set into vertical vibrations, the period will be

• A

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

• B

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

• C

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

• D

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