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THEORY OF MACHINES

25

IMPORTANT QUESTIONS

1. Explain self locking and self energized brakes.2. Derive an expression for tension ratio for band and block brake in terms of coefficient of

friction, block of contact and number of blocks in the shoe.

3. Explain rope brake dynamometer and prony brake dynamometer.4. In the differential band brake, the diameter of the drum is 900 mm, and the coefficient of

friction between the drum and the band is 0.3. The angle of contact is 240. When the force of

650 N is applied at the free end of the lever, find the maximum and the minimum force in the

band and the torque which can be applied by the brake. Take a=120 mm, b=100 mm and

l=500 mm. Assume clockwise rotation of the drum.

5. In a single block brake the drum diameter is 300 mm, the angle of contact is 90, and thecoefficient of friction between the lining and the drum is 0.3. If the operating force is 500 N

applied at the end of a lever 400 mm long, determine the torque transmitted by the brake. The

distance of the fulcrum from the center of the brake drum is 200 mm. Assume that the force

of friction passes through the fulcrum.

6. Prove for Watt governor, height of governor h = 895/N2, where N is speed of rotation ofsleeve.

7. Explain the following terms with respect to governor(1)

Sensitiveness of Governor

(2)Stability of Governor(3)Isochronous Governor(4)Hunting(5)Controlling Force(6)Effort and power of governor

8. A porter governor has equal arms each 200 mm in length and pivoted on the axis of rotation.The mass of each ball is 5 kg and the mass of sleeve is 30 kg. The radius of governor is 100

mm when governor begins to lift. If the frictional increase of speed is 1%, then determine the

governor effort and power.

9. A torsion dynamometer is fitted to a propeller shaft of a marine engine. It is found that theshaft twists 2 in a length of 20 meters at 120 r.p.m. If the shaft is hollow with 400 mm

external diameter and 300 mm internal diameter, find the power of the engine. Take modulus

of rigidity for the shaft material as 80GPa.

10.Discuss effect of gyroscopic couple on an aero plane.11.Discuss effect of gyroscopic couple on Naval ship during steering and pitching.

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THEORY OF MACHINES

12.Find the angle of inclination with respect to the vertical of a two wheeler negotiating a turn.Following data is given: combined mass of the vehicle with its rider 250 kg, moment of

inertia of the engine flywheel 0.3 kg.m2, moment of inertia of each road wheel 1 kg.m2, speed

of engine flywheel five times that of road wheels and in the same directions, height of centre

of gravity of rider with vehicle 0.6 m, two wheeler speed 90 km/h, wheel radius 300 mm,

radius of turn 50 m.

13.The turbine of rotor of a ship has mass of 3000 kg. & radius of gyration of 0.4 m, andclockwise speed of 2500 r.p.m. when looking from stern. Determine gyroscopic couple and

its effect when (i) The ship steers to the left on curve of 100 m radius at a speed of 36 km/hr.

and (ii) When the ship is pitching in S.H.M., the bow falling with its maximum velocity. The

period of pitching is 40 Sec. and the total angular displacement between the bow extreme

positions of pitching is 12.14.Explain the turning moment diagram for four stroke single cylinder engine.15.Explain the function of flywheel and explain the difference between flywheel and governor.16.A multi-cylinder engine is to run at a speed of 300 rpm. On drawing the turning moment

diagram to a scale of 1 mm = 400 N-m and 1 mm = 2.5, the areas above and below the mean

torque line in mm2

are:

+120, -175, +163, -135, +172, -199

The speed is to be kept within 1.2 % of the mean speed of the engine. Calculate the

necessary moment of inertia of the flywheel. Determine the suitable dimensions of a

rectangular flywheel rim if the breadth is twice its thickness. The density of the cast iron is7250 kg/m

3and its hoop stress is 6 MPa.

17.A constant torque 6 KW motor drives a riveting machine. A flywheel of mass 200 kg andradius of gyration 0.5 m is fitted to the riveting machine. Each riveting operation takes 1

second and requires 9000 N-m of energy. If the speed of the flywheel is 420 rpm before

riveting, find (i) the fall in speed of the flywheel after riveting and (ii) the number of rivets

fitted per hour.

18.Explain Kliens construction method.19.Explain Dynamically equivalent system and correction couple to be applied to make the tow

mass system dynamically equivalent.

20.The lengths of crank and the connecting rod of a horizontal reciprocating engine are 400 mmand 1.8 m respectively. The crank is rotating at 120 r.p.m. clockwise .The mass of the

reciprocating parts of the engine is 290 kg whereas the mass of the connecting rod is 250 kg.

The C.G. of the connecting rod is 550 mm from the crank pin centre and the radius of

gyration of the connecting rod about an axis passing through the C.G. is 650 mm .Find the

inertia torque on the crank shaft analytically and with Kliens construction, when = 40.

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21.The connecting rod of a reciprocating engine has a mass of 60 kg, distance between thebearing centers is 850 mm, diameter of small end bearing is 75 mm, diameter of big end

bearing is 100 mm, time of oscillation when the connecting rod is suspended from the small

end is 1.8 s and time of oscillation when it is suspended from the big end is 1.7 s. Determine:

(i) the radius of gyration of the connecting rod about an axis passing through the mass centre

and perpendicular to the plane of oscillation, (ii) the moment of inertia of the connecting rod

about an axis passing through its mass centre and (iii) the dynamically equivalent system of

the connecting rod comprising two masses, one at the small end bearing centre.

22.Explain two position syntheses for four bar chain mechanism and slider crank mechanism.23.Explain - function generation, path generation and motion generation.24.Using relative pole method synthesize a four bar mechanism by taking 12= 50, 12= 30,

13= 60, 13= 40. Draw again your mechanism by taking fixed link length = 60 mm.25.State Chebyshev theorem and find three precession points for the function f(x)=X1.2 in the

interval 0 X 6. Take i= 60, = 90, i= 50 and = 100.