Mechanical Vibration MCQ

81. In steady-state forced vibrations, the amplitude of vibrations at resonance is ________ damping coefficient.

1. equal to
2. directly proportional to
3. inversely proportional
4. independent of

82. Rotating shafts tend to vibrate violently at whirling speeds because

1. the shafts are rotating at vary speeds
2. bearing centre line coincide with the shaft axis
3. the system is unbalanced
4. resonance is caused due to the heavy weight of the rotor

83. In under-damped vibration system, the amplitude of vibration

1. decreases linearly with time
2. increases linearly with time
3. decreases exponentially with time
4. increases exponentially with time

84. A simple spring mass vibrating system has a natural frequency of f_n. If the spring stiffness is halved and mass is double, then the natural frequeney will become

1. f_n/2
2. 2f_n
3. 4f_n
4. 8f_n

85. The critical speed of a shaft is affected by the

1. diameter and the eccentricity of the shaft
2. span and the eccentricity of the shaft
3. diameter and the span of the shaft
4. span of the shaft

86. For a lightly damped vibrating system executing steady state forced vibration, the phase lag of displacement with respect to force at resonance is

1. 270°
2. 90°
3. 0°
4. 45°

87. Under logarithmic decrement, the amplitude of successive vibrations are

1. constant
2. in arithmetic progression
3. in geometric progression
4. in logarithmic progression