A ball with mass $0.20\,\text{kg}$, moving in the $x$-direction at speed $0.50\,\text{m s}^{-1}$, strikes a ball of mass $0.30\,\text{kg}$ that is moving in the $y$-direction at speed $0.40\,\text{m s}^{-1}$. After the collision, the two balls remain stuck together and move at an angle $\theta$ to the $x$-direction. What is the value of $\theta$?
- A$39^\circ$
- B$40^\circ$
- C$50^\circ$
- D$51^\circ$