A mass m is attached to four springs of spring constants 2.k,2k,-k and k as shown in fig. (2). The mass
 

s capable of oscillating on friction less horizontal floor. If it is displaced slightly and released then the frequency of resulting S.H.M. would be

• A

  $\frac{1}{2\mathrm{\pi }}\sqrt{\left(\frac{11\mathrm{k}}{2\mathrm{m}}\right)}$

• B

  $\frac{1}{2\mathrm{\pi }}\sqrt{\left(\frac{2\mathrm{k}}{3\mathrm{m}}\right)}$

• C

  $\frac{1}{2\mathrm{\pi }}\sqrt{\left(\frac{3\mathrm{k}}{\mathrm{m}}\right)}$

• D

  $\frac{1}{2\mathrm{\pi }}\sqrt{\left(\frac{4\mathrm{k}}{\mathrm{m}}\right)}$