$A$ simple pendulum consisting of a ball of mass $m$ tied to a thread of length $l$ is made to swing on a circular arc of angle $\theta$ in a vertical plane. At the end of this arc,another ball of mass $m$ is placed at rest. The momentum transferred to this ball at rest by the swinging ball is

• A
  Zero
• B
  $m\theta \sqrt{\frac{g}{l}}$
• C
  $\frac{m\theta}{l}\sqrt{\frac{l}{g}}$
• D
  $\frac{m}{l}2\pi \sqrt{\frac{l}{g}}$