In the arrangement shown, the pulley is light. If the reading of the spring balance S is 50 N, the acceleration of 3 kg block is $(\mathrm{g}=10 \mathrm{m}/{\mathrm{s}}^2)$

• A

  $\frac{1}{2} \mathrm{m}/{\mathrm{s}}^2$

• B

  $\frac{2}{3} \mathrm{m}/{\mathrm{s}}^2$

• C

  $\frac{4}{3} \mathrm{m}/{\mathrm{s}}^2$

• D

  $\frac{5}{3} \mathrm{m}/{\mathrm{s}}^2$