Mechanical Vibration MCQ

61. The ratio of actual damping coefficient to the critical damping coefficient is called as

  1. Magnification factor
  2. Damping factor
  3. Critical damping ratio
  4. Logarithmic decrement
Answer
Answer. b

62. When a shaking force is transmitted through the springs, damping becomes detrimental when the ratio of its frequency to the natural frequency is greater than

  1. 0.25
  2. 0.5
  3. 1
  4. $\sqrt{2}$
Answer
Answer. d

63. A simple spring-mass vibrating system has a natural frequency of N. If the spring stiffness is halved and the mass doubled, then the natural frequency will be

  1. N
  2. 0.5N
  3. 4N
  4. 2N
Answer
Answer. b

64. Critical damping is a function of

  1. Mass and stiffness
  2. Mass and damping coefficient
  3. Stiffness and natural frequency
  4. Natural frequency and damping coefficient
Answer
Answer. a

65. Consider the following statements:

Artefacts to prevent harmful effects resulting from vibrations of an unbalanced machine fixed on its foundation include.

  1. mounting the machine on springs thereby minimizing the transmission of forces
  2. using vibration isolating materials to prevent or reduce the transmission of forces
  3. moving the foundation so as to have only one degree of freedom towards reducing the transmission of forces.

Which of the above statements are correct?

  1. i and ii only
  2. i and iii only
  3. ii and iii only
  4. i, ii and iii
Answer
Answer. d

66. How is the frequency of vibrations usually expressed in

  1. Number of cycles per hour
  2. Number of cycles per minute
  3. Number of cycles per second
  4. Number of vibrations per millisecond
Answer
Answer. c

67. The speed at which the shaft runs, so that the deflection of the shaft from the axis of rotation becomes infinite, is known as

  1. whipping speed
  2. damping speed
  3. resonant speed
  4. gravitational speed
Answer
Answer. a

68. When the danger of breakage and vibration is maximum?

  1. Below the critical speed
  2. Near the critical speed
  3. Above the critical speed
  4. At the critical speed
Answer
Answer. d

69. The accurate method of finding the natural frequency of transverse vibration of a system of several loads attached to some shaft is

  1. Dunkerley method
  2. Energy method
  3. Stodola method
  4. Dunkerley and energy method
Answer
Answer. b

70. When there is a reduction in the amplitude for every cycle of vibration then the body is said to be in

  1. forced vibration
  2. undamped vibration
  3. free vibration
  4. damped vibration
Answer
Answer. d
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