Theory of Machine
Efficiency of a screw jack is given by

tan (α + φ)/tanα
tan (α - φ)/tanα
tanα/tan (α - φ)
tanα/tan (α +φ)

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Theory of Machine
For dynamic balancing of a shaft

Both (A) and (B)
None of these
The net couple due to the dynamic forces acting on the shaft is equal to zero
The net dynamic force acting on the shaft is equal to zero

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