Engineering Mechanics
Efficiency of a screw jack is given by (where α = Helix angle, and φ = Angle of friction.)

tan(α - φ)/tanα
None of these
tan(α + φ)/tanα
tanα/tan (α + φ)

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Engineering Mechanics
The total momentum of a system of masses (i. e. moving bodies) in any one direction remains constant, unless acted upon by an external force in that direction. This statement is called

Newton's second law of motion
Principle of conservation of momentum
Principle of conservation of energy
Newton's first law of motion

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