A thin rod MN, free to rotate in the vertical plane about the fixed end N, is held horizontal. When the end M is released, the speed of this end, when the rod makes an angle $$\alpha$$ with the horizontal, will be proportional to: (see figure)

A

$$\sqrt{\cos \alpha}$$

B

$$\cos \alpha$$

C

$$\sin \alpha$$

D

$$\sqrt{\sin \alpha}$$