Download PTU B.Tech 2020 March ME 7th and 8th Sem Mechanical Vibrations Question Paper

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Roll No. Total No. of Pages : 03
Total No. of Questions : 09

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B.Tech. (ME) (2012 Onwards) (Sem.-7,8)
MECHANICAL VIBRATIONS
Subject Code : BTME-803
M.Code : 71996
Time : 3 Hrs. Max. Marks : 60

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INSTRUCTIONS TO CANDIDATES :

1. SECTION-A is COMPULSORY consisting of TEN questions carrying TWO marks each.
2. SECTION-B contains FIVE questions carrying FIVE marks each and students have to attempt any FOUR questions.
3. SECTION-C contains THREE questions carrying TEN marks each and students have to attempt any TWO questions.

SECTION-A

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Q1. Answer briefly :

1. What are the main causes of vibration?
2. Define Simple Harmonic Motion.
3. State the different types of vibrations.
4. Define normal mode of vibration.

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5. What is vibration isolation?
6. Define transmissibility in a forced excitation system.
7. State the number of degrees of freedom of a continuous system.
8. A light cantilever of length ‘L’ has a mass ‘M’ fixed at its free end. What will be the frequency of lateral vibrations in the vertical plane?
9. What do you mean by critically damped system?

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10. Define the term “influence coefficient”.

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SECTION-B

Q2. What are the principles on which a vibrometer and an accelerometer are based? Explain with a neat sketch.

Q3. What is the Semi-Definite system? Derive an expression for determining the frequency of the system.

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Q4. A machine runs at 5000 rpm. Its forcing frequency is very near to its natural frequency. If the nearest frequency of the machine is at least 20% from the forced frequency, design a suitable vibration absorber for the system. Assume the mass of the machine as 30 kg.

Q5. Determine the flexibility influence coefficient for the system as shown in fig. 1. Assume E=2.1*10¹¹ N/m².

M1=20kg M2=30kg

FIG.1

Q6. A bar of length L is fixed at one end and connected at the other end by a spring of stiffness 'K' as shown in fig. 2. Derive suitable expression of motion for longitudinal vibration.

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FIG.2

SECTION-C

Q7. Derive an expression for the response of single degree of freedom system with viscous damping when it is under damped.

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Q8. Write the limitations of dynamic vibration absorber. Prove that natural frequency of centrifugal pendulum absorber is always proportional to the speed of the rotating body.

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Q9. Use Stodola’s method to determine the natural frequency of spring mass system as shown in fig. 3.

Assume m₁ =m₂=m₃=m and K₁ =K₂=K₃ =K

FIG.3

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