$A$ bar of mass $m$ resting on a smooth horizontal plane starts moving due to a constant force $F$. In the process of its rectilinear motion,the angle $\theta$ between the direction of this force and the horizontal varies as $\theta = k x$,where $k$ is a constant and $x$ is the distance traversed by the bar from its initial position. The velocity $(v)$ of the bar as a function of the angle $\theta$ is

• A
  $v = \sqrt{\frac{2 F \sin \theta}{m k}}$
• B
  $v = \sqrt{\frac{2 F}{m k \sin \theta}}$
• C
  $v = \frac{2 F \sin \theta}{m k}$
• D
  $v = \frac{2 F}{m k \sin \theta}$