JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II THEORY OF MACHINES Previous Question Paper (December - 2018 - R13)
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. Illustrate your answers with NEAT sketches wherever necessary.
Part A
Name at least four inversions of a Four – bar chain and two inversions of Double slider crank chain.
Answer
Four inversions of a four-bar chain: Beam engine (crank and lever mechanism), Coupling rod of a locomotive (double crank mechanism), Watt's indicator mechanism, and Pantograph. Two inversions of a double slider crank chain: Elliptical trammel and Scotch yoke mechanism.
If you know the magnitude, direction and sense of the velocity of the end A of a kinematic link, how do you find the velocity of the other end B using the relative velocity method?
Answer
To find the velocity of end B, draw a velocity vector representing the known velocity of A from a fixed point. Since the link is rigid, the velocity of B relative to A is perpendicular to the link AB. Draw a line through the tip of the velocity vector of A perpendicular to AB, and another line through the fixed point representing the velocity of B relative to the frame (if B is constrained). The intersection point defines the magnitude and direction of the velocity of B.
Define Diametral pitch, Pressure angle, Addendum and Clearance for the involute gear teeth.
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Explain the principle of epicyclic gear train.
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Distinguish between flat belts and V – belts.
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Define the terms: Turning moment diagram, Piston effort, Crank effort.
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Define the ‘Pitch’ of a chain drive.
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Explain the different types of friction.
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Define the term ‘Balancing of Rotating Masses’.
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Define the terms: Sensitiveness, Hunting, and Isochronism.
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Part B
Distinguish between completely constrained motion and successfully constrained motion with suitable examples.
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In a crank and slotted lever mechanism, the distance between the fixed centers is 300mm and the driving crank length is 120 mm. Find the inclination of the slotted bar with the vertical in the extreme position.
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The dimensions of the various links of the mechanism shown in Figure 1 are OA = 30 mm. AB = 75 mm, BC = 5 mm, and BD = 100 mm. The crank OA rotates at 120 rpm. Determine the velocity of slider D and angular speeds of links AB, BC and BD.
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Derive an expression for the velocity of sliding between a pair of involute gear teeth.
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Two involute gears of 20 degree pressure angle have 25 teeth each. They are required to have an arc of contact which exceeds the circular pitch by 60%. Calculate the addendum of the gears.
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In a compound gear train shown in Figure 2, the power is transmitted from a motor shaft to output shaft. The motor shaft is connected to gear 1 whereas the output shaft is connected to gear 4. The gears 2 and 3 are mounted on the same shaft. The gear 1 meshes with the gear 2 where as gear 3 meshes with gear 4. The motor shaft is rotating at 1200 r.p.m. in clockwise direction. Find the direction and speed of output shaft. (Note: Numbers on the circles are number of teeth).
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Find a relation for the coefficient of fluctuation of speed in terms of the maximum fluctuation of energy and the kinetic energy of the flywheel at mean speed.
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Find the maximum HP that can be transmitted by a belt of 16 cm × 1.5 cm cross section, if the ratio of belt tensions is 1.8, and the maximum permissible stress in the belt material is 15 kg/cm2. Density of leather may be taken as 1gm/cm3. Neglect centrifugal tension.
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In a turning moment diagram, the areas above and below the mean torque line taken in order is 4400, 1150, 1300, and 4550 mm2 respectively. The scales of the turning moment diagram are: Turning moment: 1 mm = 100 N-m; Crank angle: 1 mm = 1 degree. Find the mass of the flywheel required to keep the speed between 297 and 303 rpm, if the radius of the gyration is 0.525 m.
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Explain the effect of centrifugal tension on power transmission in belt drives.
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A square threaded screw of mean diameter 30 mm and pitch of threads 5mm is used to lift a load of 15kN by a horizontal force applied at the circumference of the screw. Find the force required if the coefficient of friction between screw and nut is 0.02.
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A pivot bearing of a shaft consists of a frustum of a cone. The diameters of the frustum are 200 mm and 400 mm, and its semi-cone angle is 60 degree. The shaft carries a load of 40 kN and rotates at 240 rpm. The coefficient of friction is 0.02. Assuming the intensity of pressure to be uniform, determine (a) magnitude of pressure, and (b) the power lost in friction.
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For a reciprocating engine, prove that: Maximum value of secondary disturbing force = (1/n) × Primary disturbing force, where n = ratio of length of connecting rod to crank length.
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The length of the upper arm of a Watt governor is 400 mm and its inclination to the vertical is 30 degree. Find the percentage increase in speed, if the balls rise by 20 mm.
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Draw the profile of a cam for the following data: A roller follower of 3 cm diameter moves outward with SHM during 160 degree of cam rotation. It rests for 20 degree of cam rotation, and returns with uniform velocity during 160 degree of cam rotation. Then it dwells for the remaining 20 degree of cam rotation. The minimum radius of cam is 5 cm, and the maximum lift of the follower is 4 cm. The cam rotates at a uniform speed in clockwise direction, and the line of stroke of the follower passes through the axis of the cam.
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