JNTU
JNTU B.Tech II DYNAMICS OF MACHINES Previous Question Paper (December - 2018 - R16)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
How the gyroscopic couple is going to be occurred?
Answer
A gyroscopic couple occurs when a rotating body (such as a flywheel or rotor) is subjected to an angular velocity about an axis perpendicular to its axis of spin. This forced change in the direction of the axis of spin results in a reactive torque, known as the gyroscopic couple, which acts to resist the change in orientation.
Where I is the moment of inertia, ω is the angular velocity of the spin, and ωₚ is the angular velocity of precession.
What is the effect of gyroscopic couple on the stability of four wheel vehicle?
Answer
The gyroscopic couple in a four-wheel vehicle arises when the vehicle takes a turn, causing the rotating parts (wheels, engine shaft, etc.) to undergo angular acceleration. The effect on stability depends on the direction of rotation of these parts:
- When the vehicle takes a turn, the gyroscopic couple acts on the frame, exerting a force that tends to lift the inner wheels and press the outer wheels against the road.
- If the engine shaft rotates in the same direction as the road wheels, the gyroscopic couple acts to increase the load on the outer wheels, which can potentially lead to overturning if the speed is high enough.
- The magnitude of the gyroscopic couple is given by C = I × ω × ωpwhere I is the total moment of inertia of the rotating parts, ω is the angular velocity of the rotating parts, and ωp is the angular velocity of precession.
- Designers often arrange the engine shaft to rotate in the opposite direction to the wheels so that the gyroscopic effect of the engine partially cancels the gyroscopic effect of the wheels, thereby enhancing the vehicle's stability during cornering.
Differentiate between single plate clutch and multi plate clutch.
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Explain about self-locking and self-energiged brake.
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Differentiate between Governor and fly wheel.
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Explain about stability and hunting of Governor.
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What is meant by primary and secondary balancing?
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What is the need of balancing rotors of high speed engines?
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What are the causes of vibrations in the members?
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What is the effect of stiffness and mass of member on the natural frequency of system?
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Part B
What is the effect of gyroscopic couple on Aeroplane?
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A flywheel of mass 10 kg and radius of gyration 18 cms is spinning about its axis, which is horizontal and is suspended at a point distant 140 mm from the plane of rotation of fly wheel. Find the angular velocity of precession of the flywheel. The spin speed of fly wheel is 1000 rpm.
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What is the effect of centrifugal couple when a vehicle moves on a cuered path?
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The total mass of a four wheeled trolley car is 2000kg. The car runs on rails of 1.5m gauge and rounds a curve of 30m radius at 40 km per hour. The truck is banked at 10°. The external diameter of wheels is 600 mm each and each pair with axle has a mass of 200 kg with radius of gyration of 250 mm. The height of the centre of mass of car above the wheel base is 100 cms. Find the pressure on each rail allowing the centrifugal force and gyroscopic couple action.
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In a screw Jack if the helix angle is α and angle of friction is φ. Derive an equation to find the condition for maximum efficiency.
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A load of 20 kN is raised by means of screw Jack. The mean diameter of the square threaded screw is 40mm and pitch is 8mm. A force of 125N is applied at the end of lever to raise the load. Determine the length of rod to be used and mechanical advantage obtained. Is the screw self locking? Take coefficient of friction as 0.1.
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Derive an expression for the friction moment of a conical pivot assuming uniform wear.
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A single plate clutch transmits 30 KW at 1000 rpm. The maximum pressure between the plates is 8.0 KN/m2. The outer diameter of the plate is 400 mm. Both sides of the plate are effective and coefficient of friction is 0.2. Determine: i) inner diameter of plate ii) axial force to engage the clutch.
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Explain about the importance of fluctuations of energy and fluctuations of speed.
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A vertical double acting steam engine develops 80 KW at 300 rpm. The maximum fluctuation of energy is 35 percent of the work done per stroke. The maximum and minimum speeds are not to vary more than 1 percent on either side of the mean speed. Find the mass of the fly wheel required, if the radius of gyration is 0.5 m.
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Differentiate between the centrifugal Governor and inertia Governor.
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What are the spring controlled Governors? Describe the function of any one of them?
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How the balancing of several masses rotating in different planes can be done?
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Four masses A, B, C and D revolve in equal radii are equally spaced along the shaft. The mass B is 8 kg and radii of C and D make angles of 90° and 250° respectively with the radius of B. Find the magnitude of masses A, C and D. And angular position of A so that the system may completely balanced.
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How the swaying couple and Hammer blow is developed in locomotives.
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How primary and secondary balancing can be done in reciprocating engines.
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Distinguish between longitudinal and transverse vibrations and explain the methods to reduce them.
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Find the natural frequency of a vibrating system having a mass suspended from the free end of a mass less spring.
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Describe three rotor vibratory system and find the ratio of their magnitudes.
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Derive an equation to find the critical speed of the shaft.
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