In a screw jack, the effort required to lift the load W is given by (where $$\alpha $$ = Helix angle and $$\varphi $$ = Angle of friction)
A
$${\text{P}} = {\text{W}}\tan \left( {\alpha - \varphi } \right)$$
B
$${\text{P}} = {\text{W}}\tan \left( {\alpha + \varphi } \right)$$
C
$${\text{P}} = {\text{W}}\tan \left( {\varphi - \alpha } \right)$$
D
$${\text{P}} = {\text{W}}\cos \left( {\alpha + \varphi } \right)$$
Correct Answer: $${\text{P}} = {\text{W}}\tan \left( {\alpha + \varphi } \right)$$
