Strength of Materials
The effort required to lift a load W on a screw jack with helix angle a and angle of friction<="" div="">

Wcos(a + )
Wtan(a-<)>)
Wtan(a + <)>)
Wsin(a + <(>)

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Strength of Materials
If a rigid body is in equilibrium under the action of three forces, then

the lines of action of these forces meet in a point
the lines of action of these forces are parallel
these forces are equal
the lines of action of these forces meet in a point & the lines of action of these forces are parallel

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