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Reg. No. : ..................................... Name : ..........................................
Third Semester B.Tech.Degree Examination, November 2009 (2008 Scheme) Branch : Industrial Engineering 08.302 : Mechanics of Machines Time : 3 Hours
Max. Marks : 100 PART – A
Answer all questions. 1. Explain the following types of Kinematic pairs. i) Lower pair ii) Screw pair 2. State Laws of Friction. 3. Sketch and explain the working of a differential brake. 4. Explain the principle of a transmission dynamometer. 5. Sketch and explain a pantograph. 6. State an prove the Law of Gearing. 7. With the help of a neat sketch of a gear profile explain the following terms : i) Pitch circle ii) Addendum 8. Derive an expression for the effort of a Poster governor. 9. Explain Raleigh’s method of vibration analysis. 10. Prove that a reciprocating mass cannot be fully balanced by a single revolving mass. (10×4=40 Marks) P.T.O.
PART – B Answer one full question from each Module. MODULE – I 11. The lengths of links of a four bar mechanism ABCD are AB = 75 mm, BC = 80 mm, CD = 37 mm and AD = 125 mm. The crank AB rotates clockwise with an angular velocity of 150 rad/s and an angular acceleration of 4000 rad/s2. The crank AB makes an angle 45° with the horizontal. Draw the velocity and acceleration diagrams for the mechanism, and determine the angular acceleration of the links BC and CD. What will be the acceleration of the mid point of link CD ? 20 12. Design a single plate clutch to transmit 30 kW at 3500 rpm, for the following specifications. Coefficient of friction
The radii ratio
The maximum pressure = 0.1 MPa Assume the plate is effective on both sides. Uniform wear conditions prevail.
MODULE – II 13. Derive an expression for the minimum number of teeth on pinion to avoid interference. Modify the result for meshing of an involute rack. 20 14. Draw a cam profile for the following specifications of a cam operating a reciprocating roller follower. Speed of cam = 250 rpm Roller follower radius = 2.6 cm Offset of the follower axes = 2 cm to the right The least radius of the cam = 5 cm Stroke of the follower = 5 cm Ascent angle = 75° Descent angle = 90° Dwell between ascent and descent = 55° Ascent and descent by uniform acceleration and retardation Also sketch the velocity and acceleration diagrams. 20
MODULE – III 15. A shaft rotating at uniform speed carries four masses 20 kg, 15 kg, 15 kg and 12 kg at radii of rotation, 5 cm, 6 cm, 7 cm and 9 cm, respectively. The second, third and fourth masses resolve in planes, 10 cm, 15 cm and 25 cm respectively measured from the plane of the first mass and are located at 60°, 120° and 270° respectively measured clockwise from the first mass when looking from this mass end of the shaft. Balance the shaft by masses located midway between those of first and second masses and midway between there of third and fourth masses. Assume the radii of rotation of the balance masses to be 5 cm each. 20 16. A shaft of 12 mm diameter carries a disc of 20 kg at the mid span and is supported is fixed bearings 0.5 m apart. The eccentricity of the mass of the disc is 0.5 mm. It the bending stress is not to exceed 150 MPa, find the range of speeds over which 20 the shaft can run safely. Take E = 2×1011 N/m2 for the shaft.