A pendulum consists of a wooden bob of mass m and length l. A bullet of mass m₁ is fired towards the pendulum with a speed v₁ and it emerges from the bob with speed $\frac{v_1}{3}$. The bob just completes motion along a vertical circle. Then, v₁ is 

• A

  $\frac{\mathrm{m}}{{\mathrm{m}}_1}\sqrt{5\mathrm{gl}}$

• B

  $\frac{3\mathrm{m}}{2{\mathrm{m}}_1}\sqrt{5\mathrm{gl}}$

• C

  $\frac{2}{3}\left(\frac{\mathrm{m}}{{\mathrm{m}}_1}\right)\sqrt{5\mathrm{gl}}$

• D

  $\frac{{\mathrm{m}}_1}{\mathrm{m}}\sqrt{\mathrm{gl}}$