Anna university-Mechanics of Machines-Question bank

REGULATIONS: 2008
MECHANICS OF MACHINES
(COMMON TO AUTOMOBILE/ AERONAUTICAL ENGG.)


PART-A                                                                                            (20*2= 40 MARKS)

ANSWER ALL QUESTIONS

1. Differentiate machine from structure.
2. Differentiate constrained kinematic chain unconstrained kinematics chain.
3. Define inversion of mechanism.
4. Write the equation for Grubler's criterion to a plane mechanism.
5. Define coefficient of friction.
6. How will you calculate average pressure in a clutch.
7. Define creep of the belt.
8. What are the disadvantages of V-belt drive over flat belt drive?
9. Define law of gearing.
10. Define reverted gear train and state its applications.
11. Define pressure angle in cam profile.
12. Draw the velocity and acceleration diagram for SHM.
13. What are the conditions for static balancing.
14. Define unbalanced force or shaking force.
15. Define hammer blow.
16. Define in-line engines.
17. Define cycle and frequency in vibration.
18. Differentiate longitudinal, transverse, and torsional vibrations.
19. Define viscous damping.
20. Define transmissibility ratio or isolation factor.

PART-B                                                                                              (5*12=60 MARKS)
ANSWER ANY FIVE QUESTIONS

21. The crank of a slider crank mechanism rotates clockwise at a constant speed of 300 rpm. The crank is 150mm and the connecting rod is 600mm long. Determine: [1] linear velocity and acceleration of the midpoint of the connecting rod, and [2] angular velocity and angular acceleration of the connecting rod, at a crank angle of 45° from inner dead center position.

22. [a] An electric motor driven power screw moves a nut in a horizontal plane against a force of 75KN at a speed of 300 mm/min. The screw has a single square thread of 6mm pitch on a major diameter of 40 mm. The coefficient of friction at the screw threads is 0.1. Estimate power of the motor. [6]

[b] The mean diameter of a square threaded screw jack is 50mm. The pitch of the thread is 10mm. The coefficient of friction is 0.15. What force must be applied at the end of a 0.7m lever, which is perpendicular to the longitudinal axis of the screw to raise a load of 20KN and to lower it? [6]

23. [a] A shaft has a number of collars integral with it. The external diameter of the collars is 400mm and shaft diameter is 250mm. If the intensity of pressure is 0.35N/sq.mm [uniform] and the coefficient of friction is 0.05, estimate: [1] power absorbed when the shaft runs at 105rpm carrying a load of 150KN; and [2] number of collars required. [6]

[b] Determine the maximum, minimum and average pressure in plate clutch when the axial force is 4KN. The inside radius of the contact surface is 50mm and the outside radius is 100mm. Assume uniform wear. [6]

24. An open belt drive connects two pulleys 1.2m and 0.5m diameter, on parallel shaft 4 meters apart. The mass of the belt is 0.9 kg per meter length and the maximum tension is not to exceed 2000N. The coefficient of friction is 0.3. The 1.2 pulley, which is the driver, runs at 200rpm. Due to slip on one of pulleys, the velocity of the driven shafts is only 450rpm. Calculate the torque on each of the two shafts, the power transmitted, and power lost in friction. What is the efficiency of the drive?

25. In an epicyclic gear train, the internal wheels A and B and compound wheels C and D rotate independently about axis O. The wheels E and F rotate on pins fixed to the arm G. E gears with A and C and F gears with B and D. All the wheels have same module and the number of teeth are: Tc=28; Td=26; Te=Tf= 18.
[1] Sketch the arrangement; [2] Find the number of teeth on A and B; [3] If the arm G makes 100rpm clockwise and A is fixed, find the speed of B; and [4] If the arm G makes 100rpm clockwise and wheel A makes 10rpm counter clockwise; find the speed of wheel B.

26. A cam drives a flat reciprocating follower in the following manner:
During first 120° rotation of the cam, follower moves outwards through a distance of 20mm with SHM. The follower dwells during next 30° of the cam rotation. During next 120° of cam rotation, the follower moves inwards with SHM. The follower dwells for next 90° of cam rotation. The minimum radius of the cam is 25mm. Draw the profile of the cam.

27. A shaft carries four masses A, B, C, and D of magnitude 200kg, 300kg, 400kg and 200kg respectively and resolving at radii 80mm, 70mm, 60mm and 80mm in planes measured from A at 300mm, 400mm and 700mm. The angles between the cranks measured anticlockwise are A to B 45°, B to C 70° and C to D 120°. The balancing masses are to be placed in planes X and Y. The distance between the planes A and X is 100mm, between X and Y is 400mm and between Y and D is 200mm. If the balancing masses revolve at a radius of 100mm, find their magnitude and angular positions.

28. The measurements on a mechanical vibrating system shows that it has a mass of 8kg and that the springs can be combined to give an equivalent spring of stiffness 5.4N/mm. If the vibrating system has a dashpot attached which exerts a force of 40N when the mass has a velocity of 1m/s, find: [1] critical damping coefficient, [2] logarithmic decrement and, [4] ratio of two consecutive amplitudes.