Vibration and Acoustics Important Questions for R23 JNTU Students
The subject Vibration and Acoustics is a critical part of the Mechanical Engineering R23 syllabus, focusing on how mechanical systems behave under oscillatory motion and how sound and noise influence machine operation. This blog covers all Vibration and Acoustics important questions — both theory and numerical — organized unit-wise to help students prepare effectively for JNTU R23 Mechanical examinations.
Vibration and AcousticsImportant Questions for R23 JNTU Students (Unit-Wise)
Unit 1: Introduction to Metallurgy and Structure of Metals
Key Theory Questions
Define vibration and classify its types with examples.
What are free, forced, and damped vibrations?
Explain natural frequency and its industrial importance.
What is resonance and how can it be avoided?
Explain degrees of freedom in vibration systems.
Define damping and list its types.
What are causes of vibration in rotating machinery?
Define logarithmic decrement and its use.
Explain energy method for determining natural frequency.
What is critical damping?
Explain vibration isolation and its engineering applications.
Define steady-state vibration.
Discuss harmonic motion and its equations.
Explain transient vibration and steady vibration.
What are engineering applications of vibration analysis?
Numerical Focus Question
A spring of stiffness 1000 N/m carries a mass of 4 kg. Find its natural frequency.
A damping force of 15 N acts on a mass moving at 2 m/s. Determine damping coefficient.
Find natural frequency in Hz for a 10 kg mass and k = 25,000 N/m.
A system with c = 20 Ns/m, m = 5 kg, and k = 800 N/m. Find damping ratio.
Determine the amplitude ratio for a forced vibration with ω/ωn = 0.75 and ζ = 0.1.
Find logarithmic decrement for a system where successive amplitudes are 1.2 cm and 0.9 cm.
A rotating shaft has mass 20 kg and stiffness 15,000 N/m. Find its critical speed.
For a spring–mass system, find energy stored per cycle for amplitude = 0.02 m.
Determine time period of oscillation for a pendulum of length 2.5 m.
Calculate maximum acceleration if amplitude = 0.01 m and frequency = 10 Hz.
UNIT 2: Single Degree of Freedom Systems
Key Theory Questions
Derive the equation of motion for an SDOF system.
What is viscous damping? Explain its behavior graphically.
Define transmissibility and explain its importance.
Explain Coulomb damping with diagrams.
What are free and forced vibrations?
Discuss response of a damped system under harmonic excitation.
Explain vibration measuring instruments like vibrometer and accelerometer.
What is vibration absorber? State its working principle.
Define stiffness and damping coefficient.
Explain dynamic magnifier.
What are rotating unbalance vibrations?
Discuss critical speeds of shafts.
Explain phase difference in vibration response.
Define base excitation and give examples.
Explain vibration isolation efficiency.
Numerical Focus Question
Find natural frequency of a 5 kg mass with spring stiffness 1250 N/m.
A system with c = 30 Ns/m, k = 2000 N/m, m = 8 kg. Find damping ratio and damped frequency.
A rotor unbalance produces 0.01 m amplitude at 600 rpm. Find stiffness if mass = 2 kg.
Determine transmissibility when ω/ωn = 0.8 and ζ = 0.15.
Find critical speed for a shaft if natural frequency = 16 Hz.
A machine weighing 1500 N is mounted on springs (k = 250,000 N/m). Find vibration isolation frequency.
A 10 kg mass vibrates with amplitude 5 mm under damping ratio 0.1. Find energy loss per cycle.
Determine phase angle between force and displacement at resonance.
For a base-excited system with amplitude ratio = 0.9, find frequency ratio.
A vibration absorber of 2 kg is attached to a 10 kg main mass. Find the tuned frequency.
UNIT 3: Multi-Degree of Freedom Systems
Key Theory Questions
Define multi-degree of freedom systems.
Explain mode shapes and natural frequencies.
What is matrix iteration method?
Define orthogonality of mode shapes.
Explain modal analysis.
What are coupled vibrations?
Discuss dynamic matrix and its properties.
Explain torsional vibrations in shafts with multiple rotors.
Define lumped parameter system.
Explain influence coefficient method.
What are principal coordinates?
Explain two-mass system.
What is mode superposition method?
Discuss determination of natural frequencies using stiffness matrix.
Explain vibration of beams and shafts as multi-DOF systems.
Numerical Focus Question
Two equal masses (3 kg each) connected with springs (k₁ = 2000, k₂ = 1500 N/m). Find natural frequencies.
Find mode shapes for a 2-DOF spring–mass system with equal stiffness.
For a torsional shaft with rotors A and B, find torsional natural frequencies if stiffness = 4000 Nm/rad.
A double pendulum has equal links (L = 1 m). Find frequencies of both modes.
Using matrix iteration, find the lowest frequency for a given 2-DOF system.
Determine amplitude ratio for coupled masses vibrating in phase.
Find equivalent stiffness for two springs connected in parallel.
Calculate dynamic response for a 3-mass system.
Determine mode participation factors for each mode.
For a system with k₁ = 3000, k₂ = 2500, m₁ = 2 kg, m₂ = 1.5 kg, find natural frequencies.
UNIT 4: Acoustics Fundamentals
Key Theory Questions
Define sound and explain its properties.
What are frequency, wavelength, and intensity?
Explain sound pressure level (SPL) and decibel scale.
What are reflection, refraction, and absorption of sound?
Define acoustic impedance.
Explain reverberation time and Sabine’s formula.
What are factors affecting room acoustics?
Define noise level and its measurement.
What is sound absorption coefficient?
Explain human ear sensitivity.
What are standing waves?
Define sound insulation and its materials.
Explain sound wave propagation.
Define frequency response and resonance in acoustics.
Discuss acoustic comfort and its importance.
Numerical Focus Question
Calculate sound intensity for SPL = 90 dB.
Find wavelength of 2000 Hz sound in air (velocity = 343 m/s).
A hall has a volume of 8000 m³ and absorption area 400 m². Find reverberation time using Sabine’s formula.
Determine SPL difference when sound intensity changes by a factor of 100.
Calculate absorption coefficient if total absorption = 200 m² and surface area = 1000 m².
A sound source produces 70 dB. Find intensity ratio compared to 50 dB.
Find sound power level for a given intensity of 10⁻⁶ W/m².
A room has volume 5000 m³ and reverberation time 1.5 s. Find total absorption.
Calculate combined SPL for two sources of 80 dB and 84 dB.
Determine sound intensity level at double the distance from the source.
UNIT 5: Noise Control and Measurement
Key Theory Questions
Define noise and its types.
Explain noise pollution and its effects.
What are sources of industrial noise?
Explain noise control at source, path, and receiver.
What are acoustic enclosures?
Discuss active and passive noise control.
Define noise barrier.
What are soundproofing materials?
Explain noise measurement standards (ISO, OSHA).
Define noise dose and equivalent sound level (Leq).
What are vibration isolation techniques for noise control?
Discuss aerodynamic noise in fans and compressors.
Explain ear protection devices.
What are sound level meters?
Describe design considerations for quiet machines.
Numerical Focus Question
Find combined noise level for sources 90 dB, 88 dB, and 85 dB.
Calculate sound intensity ratio when SPL = 70 dB and 90 dB.
If distance doubles, find reduction in sound pressure level.
Determine Leq for 80 dB (2 hr) and 90 dB (1 hr) exposure.
A room has noise level of 92 dB; find attenuation needed to reduce it to 75 dB.
Calculate transmission loss of a wall with surface density 10 kg/m² at 500 Hz.
Find overall noise exposure for multiple machines using logarithmic addition.
Determine noise reduction coefficient (NRC) for given materials.
Calculate total noise level when three identical machines each emit 85 dB.
Determine sound transmission loss if sound intensity reduces by 90%.
Preparation Tips for Vibrations and Acoustics R23 JNTU
Unit 1 & 2 → Core theory and numerical concepts (frequent in exams).
Unit 3 → Focus on multi-mass and matrix-based questions.
Unit 4 & 5 → Conceptual and practical acoustics with easy scoring numericals.
Always review previous JNTU R23 papers — many Vibration and Acoustics important questions repeat each semester.
Conclusion
The subject Vibration and Acoustics helps engineers ensure machine stability, comfort, and noise reduction. Practicing these Vibration and Acoustics important questions (R23 syllabus) — both theory and numericals — will enhance conceptual clarity and exam performance for every Mechanical Engineering student.
