This set of Machine Dynamics Multiple Choice Questions & Answers (MCQs) focuses on “Flywheel”.

1. In a four stroke I.C. engine, the turning moment during the compression stroke is

a) positive throughout

b) negative throughout

c) positive during major portion of the stroke

d) negative during major portion of the stroke

View Answer

Explanation: Since the pressure inside the engine cylinder is less than the atmospheric pressure during the suction stroke, therefore a negative loop is formed. During the compression stroke, the work is done on the gases, therefore a higher negative loop is obtained.

2. The maximum fluctuation of energy is the

a) difference between the maximum and minimum energies

b) sum of the maximum and minimum energies

c) variations of energy above and below the mean resisting torque to the

d) ratio of the mean resisting torque to the workdone per cycle

View Answer

Explanation: The difference between the maximum and the minimum energies is known as maximum fluctuation of energy.

3. The co-efficient of fluctuation of energy is the ratio of maximum energy to the minimum energy.

a) True

b) False

View Answer

Explanation: The co-efficient of fluctuation of energy is the ratio of the maximum fluctuation of energy to the work done per cycle.

4. Which of the following statement is wrong?

a) The difference between the maximum and minimum energies is called maximum fluctuation of energy.

b) The co-efficient of fluctuation of speed is the ratio of maximum fluctuation of speed to the mean speed.

c) The variations of energy above and below the mean resisting torque line is known as fluctuation of energy.

d) None of the mentioned

View Answer

Explanation: All the statements are correct.

The difference between the maximum and minimum energies is called maximum fluctuation of energy.

The co-efficient of fluctuation of speed is the ratio of maximum fluctuation of speed to the mean speed.

The variations of energy above and below the mean resisting torque line is known as fluctuation of energy.

5. The ratio of maximum fluctuation of energy to the workdone per cycle is called

a) fluctuation of energy

b) maximum fluctuation of energy

c) coefficient of fluctuation of speed

d) none of the mentioned

View Answer

Explanation: The co-efficient of fluctuation of speed is the ratio of maximum fluctuation of speed to the mean speed.

6. Maximum fluctuation of energy in a flywheel is equal to

a) Iω(ω_{1} – ω_{2})

b) Iω^{2}C_{S}

c) 2EC_{S}

d) all of the mentioned

View Answer

Explanation: None

7. A flywheel is fitted to the crankshaft of an engine having W as the amount of indicated work per revolution and permissible limits of coefficient of fluctuation of energy and speed as C_{E} and C_{S} respectively. The kinetic energy of the flywheel is given by

a) 2WC_{E}/C_{S}

b) WC_{E}/2C_{S}

c) WC_{E}/C_{S}

d) WC_{S}/2C_{E}

View Answer

Explanation: None

8. If the rotating mass of a rim type flywheel is distributed on another rim type flywheel whose mean radius is half the mean radius of the former, then energy stored in the latter at the same speed will be

a) four times the first one

b) same as the first one

c) one fourth of the first one

d) one and a half times the first one

View Answer

Explanation: None

9. The ratio of maximum fluctuation of speed to the mean speed is called

a) fluctuation of energy

b) maximum fluctuation of energy

c) coefficient of fluctuation of speed

d) none of the mentioned

View Answer

Explanation: The co-efficient of fluctuation of speed is the ratio of maximum fluctuation of speed to the mean speed.

10. The flywheel of a machine having weight of 4500 N and radius of gyration of 2 m has cyclic fluctuation of speed from 125 r.p.m to 120 r.p.m. Assuming g = 10m/s^{2}, the maximum fluctuation of energy is

a) 12822 N-m

b) 24200 N-m

c) 14822 N-m

d) 12100 N-m

View Answer

Explanation: Mass of flywheel = weight of flywheel/Acceleration due to gravity = 4500/10kg

Moment of Inertia = mk

^{2}

= 1800 kgm

^{2}

ω_{1} = 2π/60 x 125rad/sec

ω_{2} = 2π/60 x 120rad/sec

E_{max} = 1/2 I(?)^{2}

= 12087.2 N-m

= 12100 Nm

11. A circular solid disc of uniform thickness 20 mm, radius 200 mm and mass 20 kg, is used as a flywheel. If it rotates at 600 rpm, the kinetic energy of the flywheel, in Joules is

a) 395

b) 790

c) 1580

d) 3160

View Answer

Explanation: For flywheel K.E = 1/2Iω

^{2}

ω = 2πN/60 = 62.83 rad/s

I (for solid circular disk) = 1/2mR^{2} = 0.4 kg m^{2}

Hence, K.E = 790 Joules.

12. The speed of an engine varies from 210 rad/s to 190 rad/s. During the cycle the change in kinetic energy is found to be 400 Nm. The inertia of the flywheel in kg/m2 is

a) 0.10

b) 0.20

c) 0.30

d) 0.40

View Answer

Explanation: Given ω

_{1}= 210 rad/ sec, ω

_{2}= 190 rad/ sec, ΔE= 400 Nm

As the speed of flywheel changes from ω

_{1}to ω

_{2}, the maximum fluctuation of energy,

ΔE = 1/2I [(ω_{1})^{2} (ω_{2})^{2}]
I = 0.10 kgm^{2}

13. For a certain engine having an average speed of 1200 rpm, a flywheel approximated as a solid disc, is required for keeping the fluctuation of speed within 2% about the average speed. The fluctuation of kinetic energy per cycle is found to be 2 kJ. What is the least possible mass of the flywheel if its diameter is not to exceed 1 m ?

a) 40 kg

b) 51 kg

c) 62 kg

d) 73 kg

View Answer

Explanation: Given N = 1200 rpm, ΔE = 2kJ = 2000 J, D = 1m, C

_{s}= 0.02

Mean angular speed of engine,

ω = 2πN/60 = 125.66 rad/ sec

Fluctuation of energy of the flywheel is given by,

ΔE = Iω^{2}C_{s} = 1/2mR^{2}ω^{2}C_{s} For solid disc I = mR^{2}/2

m = 51 kg

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