Theory of Machine
The static balancing is satisfactory for low speed rotors but with increasing speeds, dynamic balancing becomes necessary. This is because, the

Effects of unbalances are proportional to the square of the speed
Effects of unbalances are directly proportional to the speed
Unbalanced forces are not dangerous at higher speeds
Unbalanced couples are caused only at higher speeds

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Theory of Machine
The secondary unbalanced force due to inertia of reciprocating parts in a reciprocating engine is given by (where m = Mass of reciprocating parts, ω = Angular speed of crank, r = Radius of crank, θ = Angle of inclination of crank with the line of stroke, and n = Ratio of the length of connecting rod to radius of crank)

m.ω².r (cos 2θ/n)
m.ω².r (sin 2θ/n)
m.ω².r cosθ
m.ω².r sinθ

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Theory of Machine
Which of the following statements regarding laws governing the friction between dry surfaces are correct?

The friction force is dependent on the materials of the contact surfaces.
The friction force is independent of me area of contact.
The friction force is directly proportional to the normal force.
All of these

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