In a screw jack of lead angle a, the effort required to lift the load Wis given by ........... ($$\phi$$ = Friction Angle)

A

$$P= W \tan (\alpha-\phi)$$

B

$$P= W \tan (\alpha+\phi)$$

C

$$P= W \cos (\alpha-\phi)$$

D

$$P= W \cos (\alpha+\phi)$$