A tennis ball is struck so that it leaves the racket with velocity $v$ at an angle $\theta$ above the horizontal. Its vertical velocity component is $v_y$. What is the size of the horizontal component of $v$?
- A$v\sin\theta$
- B$v_y\cos\theta$
- C$v_y\sin\theta$
- D$\sqrt{v^2 - v_y^2}$