B.E-B.E Aeronautical Engineering 3rd Sem AE 2201/111301/AE 32/ME 1204/10122 AE 302/080180006 — MECHANICS OF MACHINES(Anna University Chennai-2012)
B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2012.
Third Semester
Aeronautical Engineering
AE 2201/111301/AE 32/ME 1204/10122 AE 302/080180006 — MECHANICS OF
MACHINES
(Common to Automobile Engineering)
(Regulation 2008)
Time Three hours Maximum : 100 marks
Note : A3 size drawing sheet is to be supplied to the students.
Answer ALL questions.
PART A — (10 x 2 = 20 marks)
1. Define the Grubler's criterion for plane mechanism.
2. Name any two inversions of single slider crank chain.
3. What are the different types of friction clutches?
4. What is the effect of the velocity ratio due to the slip in the belt drive?
5. Define the following w.r.to gears (a) Circular Pitch (b) Pressure angle.
6. What are the types of followers w.r.to its nature of contact with cam?
7 What are the conditions to be satisfied for static and dynamic balancing of rotating masses?
8. What is the inclination of the crank with the line of stroke at which the primary unbalanced force is maximum?
9. Differentiate between (a) free vibration (b) forced vibration.
10. Define magnification factor.
PART B — (5 x 16 = 8O marks)
11. (a) Sketch and explain various inversions of single slider crank chain. (16)
Or
(b) The crank of a slider crank mechanism rotates clockwise at a constant speed of 300 rpm. The crank is 150 mm and the connecting rod is 600 mm long. Determine (i) linear velocity and acceleration of the midpoint of the connecting rod, and (ii) angular velocity and angular acceleration of the connecting rod, at a crank angle of 450 from inner dead centre position. (16)
12. (a) The mean diameter of the screw jack having pitch of 10 mm is 50 mm. A load of 20 kN is lifted through a distance of 170 mm. Find the work done in lifting the load and efficiency of the screw jack when
(i) the load rotates with the screw and (8)
(ii)the load rests on the loose head, which does not rotate with the screw. (8)
The external and internal diameters of the bearing surface of the loose head are 60 mm and 10 ram respectively. The coefficient of friction for the screw and nut is 0.17 and between screw and the bearing surface may be taken as 0.08.
Or
An open belt running over two pulleys 240 mm and 600 mm diameter connects two parallel shafts 3 m apart and transmits 4 kW from the smaller pulley that rotates at 300 rpm. Coefficient of friction between the belt and pulley is 0.3 and the safe working tension is 10 N per mm width.
Determine
(i) minimum width of the belt
(ii) initial belt tension, and
(iii) length of the belt required. (16)
13. (a) Two involute gears of 20° pressure angle are in mesh. The number of teeth on pinion is 20 and the gear ratio is 2. If the pitch expressed in module is 5 mm and the pitch line speed is 1.2 m/s, assuming addendum as standard and equal to one module, find :
(i) the angle turned through by pinion when one pair of teeth is in mesh; and
(ii) the maximum velocity of sliding. (16)
Or
(b) Design a cam for operating the exhaust valve of an oil engine. It is required to give equal uniform acceleration and retardation during opening and closing of the valve each of which corresponds to 60° of cam rotation. The valve must remain in the fully open position for 20° of cam rotation.
The lift of the valve is 37.5 mm and the least radius of the cam is 40 mm. The follower is provided with a roller of radius 20 mm and its line of stroke passes through the axis of the cam. (16)
14. (a) Four masses mi, mz, m3 and m4 are 200 kg, 300 kg, 240 kg and 260 kg respectively. The corresponding radii of rotation are 0.2 m. 0.15 m, 0.25 m and 0.3 m respectively and the angles between successive masses are 45°, 75° and 1350. Find the position and magnitude of the balance mass required, if its radius of rotation is 0.2 in. (16)
Or
(b) The three cylinders of an air compressor have their axes 120° to one another, and their connecting rods are coupled to a single crank. The stroke is 100 mm and the length of each connecting rod is 150 mm. The mass of the reciprocating parts per cylinder is 1.5 kg. Find the maximum primary and secondary forces acting on the frame of the compressor when running at 3000 rpm. Describe clearly a method by which such forces may be balanced. (16)
15. (a) A vertical shaft of 5 mm diameter is 200 mm long and is supported in long bearings at its ends. A disc of mass 50 kg is attached to the center of the shaft. Neglecting any increase in stiffness due to attachment of the disc to the shaft, find the critical speed of rotation and the maximum bending Stress when the shaft is rotating at 75% of the critical speed. The center of the disc is 0.25 mm from the geometric axis of the shaft. = 200 GPa. (16)
Or
(b) A single cylinder engine of total mass 200 kg is to be mounted on an elastic support which permits vibratory movement in vertical direction only. The mass of the piston is 3.5 kg and has a vertical reciprocating motion which may be assumed simple harmonic with a stroke of 150 mm. It is desired that the maximum vibratory force transmitted through the elastic support to the foundation shall be 600 N when the engine speed is 800 rpm and less than this at all higher speeds. (i) Find the necessary stiffness of the elastic support, and the amplitude of vibration at 800 rpm and (ii) If the engine speed is reduced below 800 rpm, at what speed will the transmitted force again becomes 600 N. (16)
| Earning: ₹ 7.00/- |
