Mcq Of Dynamics Of Machinery-2161901 PDF

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MULTIPLE CHOICE QUESTIONS SUBJECT: DYNAMICS OF MACHINERY SUBJECT CODE: 2161901

Module 1: Balancing of Rotating Masses 1. Often an unbalance of forces is produced in rotary or reciprocating machinery due to the

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a) Centripetal forces b) Centrifugal forces c) Friction forces d) Inertia forces Which of the following is true for centrifugal force causing unbalance? a) Direction changes with rotation b) Magnitude changes with rotation c) Direction and magnitude both change with rotation d) Direction and magnitude both remain unchanged with rotation In a revolving rotor, the centrifugal force remains balanced as long as the centre of the mass of the rotor lies a) Below the axis of shaft b) On the axis of the shaft c) Above the axis of shaft d) Away from the axis of shaft If the unbalanced system is not set right then. a) Static forces develop b) Dynamic forces develop c) Tangential forces develop d) Radial forces develop What is not the effect of unbalanced forces? a) Load on bearings b) Dangerous vibrations c) Stresses in various members d) Violation of conservation of mass principle What is the effect of a rotating mass of a shaft on a system? a) Bend the shaft b) Twist the shaft c) Extend the shaft d) Compress the shaft

7. Let the disturbing mass be 100 kg and the radius of rotation be 20 cm and the rotation speed be 50 rad/s, then calculate the centrifugal force in kN. a) 50 b) 25 c) 50000 d) 25000 8. The mass used to balance the mass defect is known as a) Balancing mass b) Defect mass c) Replacement mass d) Fixing mass 9. Let the centrifugal force in kN be 25 and the radius of rotation be 20 cm and the rotation speed be 50 rad/s, then calculate the mass defect in Kg. a) 50 b) 25 c) 50000 d) 25000 10. If all the masses are in one plane, then what is the maximum no. of masses which can be placed in the same plane? a) 3 b) 4 c) 6 d) No limitation 11. In balancing of single-cylinder engine, the rotating unbalance is a) completely made zero and so also the reciprocating unbalance b) completely made zero and the reciprocating unbalance is partially reduced c) partially reduced and the reciprocating unbalance is completely made zero d) partially reduced and so also the reciprocating unbalance 12. Which of the following statements is correct about the balancing of a mechanical system? a) If it is under static balance, then there will be dynamic balance also b) If it is under dynamic balance, then there will be static balance also c) Both static as well as dynamic balance have to be achieved separately d) None of the mentioned 13. The balancing of rotating and reciprocating parts of an engine is necessary when it runs at (a) Slow speed (b) Medium speed (c) High speed (d) None of above

14. For static balancing of a shaft, (a) The net dynamic force acting on the shaft is equal to zero (b) The net couple due to the dynamic forces acting on the shaft is equal to zero (c) Both (a) and (b) (d) None of the above 15. For dynamic balancing of a shaft, (a) The net dynamic force acting on the shaft is equal to zero (b) The net couple due to dynamic forces acting on the shaft is equal to zero (c) Both (a) and (b) (d) None of the above 16. In order to have a complete balance of the several revolving masses in different planes (a) The resultant force must be zero (b) The resultant couple must be zero (c) Both the resultant force and couple must be zero (d) None of the above 17. Determine magnitude of balancing mass required if 250 mm is the radius of rotation. Masses of A, B and C are 300 kg, 250 kg and 100 kg which have radii of rotation as 50 mm, 80 mm and 100 mm respectively . The angles between the consecutive masses are 110o and 270o respectively. (a) 45.36 kg (b) 47.98 kg (c) 40.50 kg (d) None of the above 18. Which of the following factors are not responsible for unbalancing in rotating systems? (a) Errors (b) Tolerances (c) Shape of the rotor (d) None of the above 19. Which of the following conditions should be satisfied for static balancing? 1. Dynamic forces acting on the system should be zero 2. Couple acting on the system due to dynamic force should be zero 3. Centrifugal forces acting on the system should be zero 4. Couple acting on the system due to centrifugal forces should be zero (a) Condition 1 and condition 2 (b) Condition 1 and condition 3 (c) Condition 3 and condition 4 (d) All of the above

20. Which formula is used to calculate mass moment of inertia (IG) of a circular rim about the axis through centre of gravity? (a) mr2/2 (b) mr2/12 (c) mr2/4 (d) mr2 21. The static balancing is satisfactory for low speed rotors but with increasing speeds, dynamic balancing becomes necessary. This is because, the (a) unbalanced couples are caused only at higher speeds (b) unbalanced forces are not dangerous at higher speeds (c) effects of unbalances are proportional to the square of the speed (d) effects of unbalances are directly proportional to the speed 22. A system in dynamic balance implies that (a) the system is critically damped (b) there is no critical speed in the system (c) the system is also statically balanced (d) there will absolutely no wear of bearings 23. The unbalanced force due to revolving masses (a) varies in magnitude but constant in direction (b) varies in direction but constant in magnitude (c) varies in magnitude and direction both (d) constant in magnitude and direction both 24. Two systems shall be dynamically equivalent when (a) The mass of two are same (b) C.G. of two coincides (c) M.I. of two about an axis through e.g. is equal (d) All of the above 25. A rotor supported at A and B carries two masses as shown in the below figure. The rotor is, (a) Dynamically balanced (b) Statically balanced (c) Statically and dynamically balanced (d) Not balanced

Module 2: Balancing of Reciprocating Engines 1. The magnitude of swaying couple due to partial balance of the primary unbalancing force in locomotive is a) inversely proportional to the reciprocating mass b) directly proportional to the square of the distance between the centre lines of the two cylinders c) inversely proportional to the distance between the centerlines of the two cylinders d) directly proportional to the distance between the centerlines of the two cylinders 2. In a locomotive, the ratio of the connecting rod length to the crank radius is kept very large in order to a) minimize the effect of primary forces b) minimize the effect of secondary forces c) have perfect balancing d) start the locomotive conveniently 3. Multi-cylinder engines are desirable because a) only balancing problems are reduced b) only flywheel size is reduced c) both (a) and (b) d) none of the mentioned 4. When the primary direct crank of a reciprocating engine makes an angle θ with the line of stroke, then the secondary direct crank will make an angle of .......... with the line of stroke. a) θ/2 b) θ c) 2θ d) 4θ 5. The primary unbalanced force is maximum, when the angle of inclination of the crank with the line of stroke is (a) 0° (b) 90° (c) 180° (d) 360° 6. The partial balancing means (a) Balancing partially the revolving masses (b) Balancing partially the reciprocating masses (c) Best balancing of engines (d) All of the above

7. In order to facilitate the starting of locomotive in any position, the cranks of a locomotive, with two cylinders, are placed at to each other. (a) 45° (b) 90° (c) 120° (d) 180° 8. In a locomotive, the ratio of the connecting rod length to the crank radius is kept very large in order to (a) Minimise the effect of primary forces (b) Minimise the effect of secondary forces (c) Have perfect balancing (d) Start the locomotive quickly 9. The swaying couple is maximum or minimum when the angle of inclination of the crank to the line of stroke is equal to (a) 45° and 135° (b) 90° and 135° (c) 135° and 225° (d) 45° and 225° 10. The tractive force is maximum or minimum when the angle of inclination of the crank to the line of stroke is equal to (a) 90° and 225° (b) 135° and 180° (c) 180° and 225° (d) 135° and 315° 11. The swaying couple is due to the (a) Primary unbalanced force (b) Secondary unbalanced force (c) Two cylinders of locomotive (d) Partial balancing 12. In a locomotive, the maximum magnitude of the unbalanced force along the perpendicular to the line of stroke, is known as (a ) Tractive force (b) Swaying couple (c) Hammer blow (d) None of these

13. The effect of hammer blow in a locomotive can be reduced by (a) Decreasing the speed (b) Using two or three pairs of wheels coupled together (c) Balancing whole of the reciprocating parts (d) Both (a) and (b) 14. Which of the following statement is correct? (a) In any engine, 100% of the reciprocating masses can be balanced dynamically (b) In the case of balancing of multicylinder engine, the value of secondary force is higher than the value of the primary force (c) In the case of balancing of multimass rotating systems, dynamic balancing can be directly started without static balancing done to the system (d) None of the above. 15. Secondary forces in reciprocating mass on engine frame are (a) Of same frequency as of primary forces (b) Twice the frequency as of primary forces (c) Four times the frequency as of primary forces (d) None of the above 16. If c be the fraction of the reciprocating parts of mass m to be balanced per cyclinder of a steam locomotive with crank radius r, angular speed ω, distance between centre lines of two cylinders a, then the magnitude of the maximum swaying couple is given by a) 1 – c / 2 mrω2a b) 1 – c / √2mrω2a c) √2(1 – c)mrω2a d) none of the mention 17. What is the total no. of cylinders in a locomotive having crank at right angles? a) 1 b) 2 c) 3 d) 4 18. 3. In an inside cylinder locomotive, the position of the driving wheels is a) Outside cylinder b) Inside cylinder c) Down to cylinder d) Above the cylinder

19. In an outside cylinder locomotive, the position of the driving wheels is a) Outside cylinder b) Inside cylinder c) Down to cylinder d) Above the cylinder 20. A single or uncoupled locomotive is one, in which the effort is transmitted to a) Both the pair of wheels b) Alternatively between the wheels c) One pair of wheels d) Neither of the wheels 21. In coupled locomotives, the driving wheels are connected to the leading and trailing wheel by an coupling rod. a) Inside b) Outside c) Sideway d) Bottom 22. What is the effect of partial balancing of the reciprocating parts? a) Unbalanced primary force b) Unbalanced secondary force c) Balanced primary force d) Balanced secondary force 23. The effect of an unbalanced primary force along the line of stroke is to produce a) Swaying couple b) Constant tractive force c) Piston effort d) Crank effort 24. The effect of an unbalanced primary force perpendicular to the line of stroke is to produce a) Variation in pressure on the rails b) Variation in tractive force c) Swaying couple d) Piston effort 25. What is the effect of variation of pressure on the rails? a) Hammering action b) Piston effort c) Variation in tractive force d) Swaying couple

26. Hammering action on the rails is caused by a) Variation of pressure on the rails b) Variation of temperature on the rails c) Variation of thermal diffusibility of the rails d) Variation of crank effort 27. At which of the following angles in degrees does the tractive force attains a minimum value? a) 315 b) 45 c) 90 d) 60 28. At which of the following angles in degrees does the tractive force attains a maximum value? a) 135 b) 45 c) 90 d) 60 29. Which of the following has a tendency to sway engine in alternately in clockwise and anticlockwise directions? a) Swaying couple b) Tractive force c) Hammer blow d) Hammer couple 30. At which of the following angles in degrees does the swaying couple attains a maximum value? a) 135 b) 45 c) 90 d) 60 31. If the maximum value occurs at 45 degrees then at which of the following angles in degrees will the swaying couple attains its maximum value again? a) 135 b) 45 c) 225 d) 60

32. A V-twin engine has the cylinder axes at 90 degrees and the connecting rods operate a common crank. The reciprocating mass per cylinder is 23 kg and the crank radius is 7.5 cm. The length of the connecting rod is 0.3 m. If the engine is rotating at the speed is 500 r.p.m. What is the value of maximum resultant secondary force in Newtons? a) 7172 b) 1672 c) 1122 d) 1272 33. From the following data of a 60 degree V-twin engine, determine the minimum value for primary forces in Newton: Reciprocating mass per cylinder = 1.5 Kg, Stroke length = 10 cm, Length of connecting rod = 25 cm, Engine speed = 2500 rpm a) 7711 b) 4546 c) 2570 d) 8764 34. The essential condition of placing the two masses, so that the system becomes dynamically equivalent, is (where l1 and l2 = Distance of two masses from the centre of gravity of the body, and kG = Radius of gyration of the body) (a) l1 = kG (b) l2 = kG (c) l1l2 = kG (d) l1l2 = kG2 35. In a reciprocating engine, usually of the reciprocating masses are balanced. (a) one-half (b) two-third (c) three-fourth (d) whole 36. The unbalanced force due to reciprocating masses (a) varies in magnitude but constant in direction (b) varies in direction but constant in magnitude (c) varies in magnitude and direction both (d) constant in magnitude and direction both 37. Which of the following statement is correct? (a) The primary unbalanced force is less than the secondary unbalanced force. (b) The primary unbalanced force is maximum twice in one revolution of the crank. (c) The unbalanced force due to reciprocating masses varies in magnitude and direction. (d) The magnitude of swaying couple in locomotives is inversely proportional to the distance between the two cylinder centre lines.

38. A system of masses rotating in different parallel planes is in dynamic balance if the (a) resultance force is equal to zero (b) resultant couple is equal to zero (c) resultant force and resultant couple are both equal to zero (d) resultant force is numerically equal to the resultant couple, but neither of them need necessarily be zero 39. The primary unbalanced force due to inertia of reciprocating parts in a reciprocating engine is given by (where m = Mass of reciprocating parts, ω = Angular speed of crank, r = Radius of crank, θ = Angle of inclination of crank with the line of stroke, and n = Ratio of the length of connecting rod to radius of crank) (a) m.ω².r sinθ (b) m.ω².r cosθ (c) m.ω².r (sin 2θ/n) (d) m.ω².r (cos 2θ/n) 40. The secondary unbalanced force is maximum when the angle of inclination of the crank with the line of stroke is (a) 0° and 90° (b) 180° and 360° (c) Both (A) and (B) (d) None of these 41. The tractive force in a locomotive with two cylinders is given by (where c = Fraction of reciprocating parts per cylinder, m = Mass of reciprocating parts, ω = Angular speed of crank, r = Radius of crank, and θ = Angle of inclination of crank to the line of stroke) (a) m.ω².r cosθ (b) c.m.ω².r sinθ (c) (1 - c).m.ω².r (cosθ - sinθ) (d) m.ω².r (cosθ - sinθ) 42. The unbalanced primary forces in a reciprocating engine are (a) Balanced completely (b) Balanced partially (c) Balanced by secondary forces (d) Not balanced

43. For a twin cylinder V-engine, the crank positions for primary reverse cranks and secondary direct cranks are shown in the below figure. The engine is a, (a) 30° V-engine (b) 60° V-engine (c) 120° V-engine (d) 150° V-engine

44. A rigid body, under the action of external forces, can be replaced by two masses placed at a fixed distance apart. The two masses form an equivalent dynamical system, if (a) The sum of the two masses is equal to the total mass of body (b) The center of gravity of the two masses coincides with that of the body (c) The sum of mass moment of inertia of the masses about their center of gravity is equal to the mass moment of inertia of the body (d) All of the above 45. Inertia force acts (a) Perpendicular to the acceleration force (b) Along the direction of acceleration force (c) Opposite to the direction of acceleration force (d) None of the above 46. A rotor which is balanced statically but not dynamically is supported on two bearings L apart and at high speed of the rotor, reaction on the left bearing is R. The right side of the bearing is shifted to a new position 2L apart from the left bearing. At the same rotor speed, dynamic reaction on the left bearing in the new arrangement will (a) Remain same as before (b) Become equal to 2R (c) Become equal to R/2 (d) Become equal to R/4

Module 3: Mechanical Vibrations 1. The ratio of the actual damping coefficient to the critical damping coefficient is called . (a) Damping factor (b) Resonance (c) Critical damping (d) Natural frequency 2. When a body moves with simple harmonic motion, the product of its periodic time and frequency is equal to (a) zero (b) one (c) π/2 (d) π 3. In a vibrating system, if the actual damping coefficient is 40 N/m/s and critical damping coefficient is 420 N/m/s, then logarithmic decrement is equal to (a) 0.2 (b) 0.4 (c) 0.6 (d) 0.8 4. If ω/ωn is very high for a body vibrating under steady state vibrations, the phase angle for all values of damping factors, will tend to approach (a) 0° (b) 90° (c) 180° (d) 360° 5. The factor which affects the critical speed of a shaft is (a) Diameter of disc (b) Span of shaft (c) Eccentricity (d) All of these 6. In vibration isolation system, the transmissibility will be equal to unity, for all values of damping factor, if ω/ωn is (a) Equal to one (b) Equal to √2 (c) Less than √2 (d) Greater than √2

7. If ω/ωn = 2, where co is the frequency of excitation and ωn is the natural frequency of vibrations, then the transmissibility of vibration will the (a) 0.5 (b) 1 (c) 1.5 (d) 2 8. In under damped vibrating system, the amplitude of vibration (a) Decreases linearly with time (b) Increases linearly with time (c) Decreases exponentially with time (d) Increases exponentially with time 9. The frequency of damped vibrations with viscous damping is the frequency of undamped vibrations. (a) more than (b) less than (c) same as 10. A mass of 1 kg is attached to the end of a spring with a stiffness of 0.7 N/mm. The critical damping coefficient of this system is (a) 1.4 N-s/m (b) 18.52 N-s/m (c) 52.92 N-s/m (d) 529.2 N-s/m 11. A reed type tachometer use the principle of (a) longitudinal vibration (b) torsional vibration (c) transverse vibration (d) damped free vibration 12. Which of the following statement is correct ? (a) The periodic time of a particle moving with simple harmonic motion is the time taken by a particle for one complete oscillation. (b) The periodic time of a particle moving with simple harmonic motion is directly proportional to its angular velocity. (c) The velocity of a particle moving with simple harmonic motion is zero at the mean position. (d) The acceleration of the particle moving with simple harmonic motion is maximum at the mean position.

13. The natural frequency of free longitudinal vibrations is equal to (where m = Mass of the body, s = Stiffness of the body, and δ = Static deflection of the body). (a) (b) (c)

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(d) any one of these 14. In order to double the period of a simple pendulum, the length of the string should be (a) Halved (b) Doubled (c) Quadrupled (d) None of these 15. When a rigid body is suspended vertically and it oscillates with a small amplitude under the action of the force of gravity, the body is known as (a) simple pendulum (b) compound pendulum (c) torsional pendulum (d) second's pendulum 16. Longitudinal vibrations are said to occur when the particles of a body moves (a) perpendicular to its axis (b) parallel to its axis (c) in a circle about its axis (d) none of these 17. If the damping factor for a vibrating system is unity, then the system will be (a) over damped (b) under damped (c) critically damped (d) without vibrations 18. In vibration isolation system, if ω/ωn < 2, then for all values of damping factor, the transmissibility will be (where ω = Angular speed of the system, ωn = Natural frequency of vibration of the system) (a) less than unit...