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# Machine Foundations – Mass Spring System

Most of the motions encountered in soil dynamics are __________

a) Plane linear motion

b) Motion by impact

c) Horizontal motion

d) All of the mentioned

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Answer: a

Explanation: Most of the motions encountered in soil dynamics work are those of vibration, plane linear motion, a motion brought about by impact, shock, elastic waves, and seismic action of geophysical forces.

The theory of harmonic vibrations is applicable to _________ for designing of foundation.

a) Turbines

b) Motors

c) Generators

d) All of the mentioned

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Answer: d

Explanation: The design of foundations of turbines, motors, generators, compressor, forge hammers and other machine having a rhythmic application of unbalanced forces requires special knowledge of the theory of harmonic vibrations.

The constituent part of soil mechanics which deals with soil under dynamic condition is _______

a) Mass spring system

b) Soil dynamics

c) Soil system

d) Mass system

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Answer: b

Explanation: Soil dynamics is defined as that constituent part of soil mechanics which deals with soil under dynamic conditions.

The factor responsible for additional dynamic load in rotating machines are ________

a) Static load and Inertial force

b) Geophysical force

c) None of the mentioned

d) All of the mentioned

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Answer: a

Explanation: Inertial forces of rotating elements of machines contribute besides their static loads, additional dynamic loads.

In soil dynamics problems, the analysis may be conveniently carried out by ___________

a) Spring mass system

b) Inertial force

c) Free vibration

d) Amplitude test

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Answer: a

Explanation: In soil dynamic problems, the analysis may be conveniently carried out by a single equivalent mass supported by a perfectly elastic system or spring mass system.

The mass spring system has ________ degrees of freedom.

a) 4

b) 3

c) 6

d) 5

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Answer: c

Explanation: The elastic spring system has six natural frequencies and thus has six degrees of freedom.

The time for one complete oscillation of the mass in the spring system is called _________

a) Amplitude

b) Time period

c) Free period

d) Frequency interval

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Answer: c

Explanation: The time for one complete oscillation of the mass is called the free period and the distance up or down from the equilibrium position is called the amplitude.

Which of the following expression is called the equation of motion?

a) fn = k / m

b) z + ωn2 z = 0

c) m z + ωn2 z = 0

d) k z + k / m = 0

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Answer: b

Explanation: The equation of motion is given by the following formula

z + ωn2 z = 0

Where, m = mass of the vibrating body

Z = acceleration

ωn = natural frequency of the system.

For an oscillatory machine, the force can be expressed as _________

a) Cosine function and Sine function

b) Cosec function

c) None of the mentioned

d) All of the mentioned

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Answer: a

Explanation: Generally for an oscillatory machine (where the machinery vibrates because an unbalanced rotational force exists), the force can be expressed as a sine or cosine function, such as F0sinωt.