Two blocks of mass 2 kg are connected by a massless ideal spring of spring constant k = 10 N/m. The upper block is suspended from roof by a light string A. The system shown is in equilibrium. The string A is now cut, the acceleration of upper block just after the string A is cut will be $\left(g=10\mathrm{m}/{\mathrm{s}}^2\right)$

• A

  $0\mathrm{m}/{\mathrm{s}}^2$

• B

  $10\mathrm{m}/{\mathrm{s}}^2$

• C

  $15\mathrm{m}/{\mathrm{s}}^2$

• D

  $20\mathrm{m}/{\mathrm{s}}^2$