Theory of Machine
A thin circular disc is rolling with a uniform linear speed, along a straight path on a plane surface. Which of the following statement is correct in this regard?

The centre of the disc has centrifugal acceleration
The centre of the disc has zero acceleration
All points of the disc have the same velocity
The point on the disc making contact with the plane surface has zero acceleration

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Theory of Machine
The primary 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 cosθ
m.ω².r sinθ
m.ω².r (cos 2θ/n)
m.ω².r (sin 2θ/n)

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

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

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