# Mechanical vibration MCQ Mechanical Engineering

50 Questions 30 Mins

Mechanical vibration is a phenomenon that can occur in any system with mass and stiffness. In most cases, it's an undesired effect that can cause damage to equipment or lead to other safety issues. It's important to be aware of the causes and effects of mechanical vibration so that you can take steps to prevent it from happening in your own systems.

There are two main types of mechanical vibration: free vibration and forced vibration. Free vibration occurs when a system is set in motion by an initial force, but there is no external force acting on the system after that. Forced vibration happens when there is an external force acting on the system while it's in motion. The most common cause of forced vibration is an unbalanced force, such as when a machine is running off-center.

There are several ways to prevent mechanical vibration from occurring in your systems. One way is to make sure that all of the moving parts in your system are properly balanced. Another way is to use damping devices, which absorb energy and reduce vibration. If you're already experiencing vibration, you can try to reduce it by changing the frequency of the vibrating component or by adding mass to the system.

Following are some of the multiple choice questions on the Mechanical vibration with answers that will help the students in developing their knowledge.

## Mechanical vibration MCQ

• 60
• 75
• 80
• 100

### 2. The transmitted force through a mass-spring damper system will be greater than the transmitted through rigid supports for all values of damping factors, if the frequency ratio ωωn\frac{\omega}{\omega_n}ωn​ω​ is

• more than  2\sqrt{2}2​
• less than  2\sqrt{2}2​
• equal to one
• less than one

### 3. For a harmonically excited single degree of freedom viscous damped system, which one of the following is correct?

• Inertia force leads damping force by 90° while damping force leads spring force by 90°
• Spring force leads damping force by 90° while damping force leads inertia force by 180°
• Spring force and damping force are in phase, and inertia force leads them by 90°
• Spring force and inertia force are in phase, and damping force leads them by 90°

• 1.2
• 3.4
• 8.7
• 12

• 1 & 2
• 2 & 3
• 3 & 1
• 1, 2 & 3

• 1
• 10
• 100
• infty ∞

### 7. In a forced vibration with viscous damping, maximum amplitude occurs when forced frequency is

• Equal to natural frequency
• Slightly less than natural frequency
• Slightly greater than natural frequency
• Zero

• 0.25
• 0.5
• 1
• √2

### 9. The rotor of a turbine is generally rotated at

• the critical speed
• a speed much below the critical speed
• a speed much above the critical speed
• a speed having no relation to critical speed

### 10. For steady-state forced vibrations, the phase lag at resonance is

• 0°0\degree0°
• 45°45\degree45°
• 90°90\degree90°
• 180°180\degree180°

### 11. Rotating shafts tend of vibrate violently at whirling speeds because

• the shafts are rotating at very high speeds
• Bearing centre line coincides with the shaft axis
• The system is unbalanced
• Resonance is caused due to the heavy weight of the rotor

### 12. A slender shaft supported on two bearings at its ends carries a disc with an eccentricity e from the axis of rotation. The critical speed of the shaft is N. If the disc is replaced by a second one of same weight but mounted with an eccentricity 2e, critical speed of the shaft in the second case is

• N2\frac{N}{2}2N​
• N2\frac{N}{\sqrt{2}}2​N​
• NNN
• 2N2N2N

• 1
• 1.6
• 2
• 2.4

### 14. A viscous damping system with free vibrations will be critically damped if the damping factor is

• Zero
• Less than one
• Equal to one
• Greater than one

### 15. In a multi-rotor system of torsional vibration maximum number of nodes that can occur is

• two
• equal to the number of rotor plus one
• equal to the number of rotors
• equal to the number of rotors minus one

### 16. During torsional vibration of a shaft, the node is characterized by the

• maximum angular velocity
• maximum angular displacement
• maximum angular acceleration
• zero angular displacement

• 5367 rpm
• 6000 rpm
• 9360 rpm
• 12000rpm

• N
• 0.408N
• 0.204N
• 0.167N

### 19. In a system subjected to damped forced vibrations, the ratio of maximum displacement to the static deflection is known as

• Critical damping ratio
• Damping factor
• Logarithmic decrement
• Magnification factor

### 20. When the mass of a critically damped single degree of freedom system is deflected from its equilibrium position and released, it will

• Oscillate with increasing time period
• Oscillate with decreasing amplitude
• Oscillate with constant amplitude.

• 1 or above
• 0.5
• 0.3
• 0.866

• 0.223
• 17.88
• 71.4
• 223.6

### 23. Under logarithmic decrement, the amplitude of successive vibrations are

• Constant
• in arithmetic progression
• In geometric progression
• in logarithmic progression

• 36
• 6
• 9
• 0

### 25. Logarithmic decrement of a damped single degree of freedom system is δ\deltaδ .If the stiffness of the spring is doubled and the mass is made half, then the logarithmic decrement of the new system will be equal to

• δ​ ( delta )
• 1/2 δ​ ( delta )
• 2δ​ ( delta )
• None of these

### 26. md2xdt2+cdxdt+kx=Fosin⁡(ωt)m\frac{\text{d}^2x}{\text{d}t^2}+c\frac{\text{d}x}{\text{d}t}+kx=F_o\sin\left(\omega t\right)mdt2d2x​+cdtdx​+kx=Fo​sin(ωt) is the equation of motion of a system. The steady state frequency at which the system will oscillate

•  km\sqrt{\frac{k}{m}}mk​​
•  km+ω\sqrt{\frac{k}{m}}+\omegamk​​+ω
•  ω\omegaω
• Data insufficient

### 27. Transmissibility is unity at two points. Which one of the following is true for these two points? r=\frac{\omega}{\omega_n}r=ωn​ω​

• r is zero and  3\sqrt{3}3​  for all values of damping
• r is zero and  2\sqrt{2}2​  for all values of damping
• r is unity and  3\sqrt{3}3​  for all values of damping
• r is unity and  2\sqrt{2}2​  for all values of damping

• 0.25
• 0.5
• 0.75
• 1.0

### 29. A vehicle suspension system consists of a spring and a damper. The stiffness of the spring is 3.6 kN/m and constant of the damper is 400 Ns/m. If the mass is 50 kg, then the damping factor and damped natural frequency (in Hz), respectively, are

• 0.471 and 1.19 Hz
• 0.471 and 7.48 Hz
• 0.666 and 1.35 Hz
• 0.666 and 8.5 Hz

• 10
• 20
• 30
• 40

• 1/2
• 3/4
• 4/3
• 2

### 32. The critical speed of a rotating shaft depends upon

• Mass
• stiffness
• mass and stiffness
• mass, stiffness and eccentricity

• 810
• 900
• 800
• 820

• 6040
• 3020
• 1424
• 955

### 35. A spring-mass suspension has a natural frequency of 40 rad/s. What is the damping ratio required if it is desired to reduce this frequency to 20 rad/s by adding a damper to it?

• 32\frac{\sqrt{3}}{2}23​​
• 12\frac{1}{2}21​
• 12\frac{1}{\sqrt{2}}2​1​
• 14\frac{1}{4}41​

### 36. A machine mounted on a single coil spring has a period of free vibration of T. If the spring is cut into four equal parts and placed in parallel and the machine is mounted on them, then the period of free vibration of the new system will become.

• 16T
• 4T
• T4\frac{T}{4}4T​
• T16\frac{T}{16}16T​

### 37. If air resistance is neglected, while it is executing small oscillations the acceleration of the bob of a simple pendulum at the mid-point of its swing will be

• zero
• a minimum but not equal to zero
• a maximum
• not determinable unless the length of the pendulum and the mass of the bob are known

• 50
• 20
• 10
• 5

• 0.0531
• 0.9922
• 0.0162
• 0.0028

• 2
• 4
• 8
• √8 * wn