Theory of Machine
In a screw jack, the effort required to lift the load W is given by (where α = Helix angle, and φ = Angle of friction)

P = W tan(φ - α)
P = W tan(α - φ)
P = W cos(α + φ)
P = W tan(α + φ)

ANSWER DOWNLOAD EXAMIANS APP

Theory of Machine
Lower pairs are those which have

Surface contact between the two elements when in motion
Two elements that permit relative motion
Elements of pairs not held together mechanically
Point or line contact between the two elements when in motion

ANSWER DOWNLOAD EXAMIANS APP