In a screw jack, the effort required to lower the load W is given by
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. $${\text{P}} = {\text{W}}\cos \left( {\alpha + \varphi } \right)$$
Answer: Option C

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