Theory of Machine
The natural frequency of free longitudinal vibrations is equal to (where m = Mass of the body, s = Stiffness of the body, and δ = Static deflection of the body)

1/2π × √(g/δ)
1/2π × √(s/m)
Any one of the listed here
0.4985/√δ

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Theory of Machine
In a mechanism, the fixed instantaneous centers are those centers which

Vary with the configuration of the mechanism
None of the listed here
Remain in the same place for all configurations of the mechanism
Moves as the mechanism moves, but joints are of permanent nature

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