Quiz: Mechanical Engineering

Exam: AE/JE

Topic: Miscellaneous

Each question carries 1 mark

Negative marking: 1/4 mark

Time: 10 Minutes

Q1. In gramophones for adjusting the speed of the turntable, the following type of governor is commonly employed

(a) Hartung governor

(b) Wilson Hartnell governor

(c) Pickering governor

(d) Inertia governor

Q2. The stiffness of the spring in a Hartnell governor is equal to,

Where

S1 = Spring force exerted on the sleeve at maximum radius of rotation.

S2 = Spring force exerted on the sleeve at minimum radius of rotation.

h = lift of sleeve

(a) S1 – S2/2h

(b) S1 + S2/h

(c) S1 – S2/h

(d) 2(S1 – S2)/2h

Q3. In descending order of magnitude, the thermal conductivity of

- Pure iron
- Water
- Saturated water vapor
- Pure aluminium

Can be arranged as

(a) 1, 2, 3, 4

(b) 2, 3, 1, 4

(c) 4, 1, 2, 3

(d) 4, 3, 1, 2

Q4. Consider the following statements:

The Fourier heat conduction equation

Q=-kA dt/dx

Presumes

- Steady state conditions
- Constant value of thermal conductivity
- Uniform temperature at the wall surfaces
- One-dimensional heat flow

Which of these statements are correct?

(a) 1, 2 and 3

(b) 1,2 and 4

(c) 2, 3 and 4

(d) 1, 3 and 4

Q5. Which one of the following statements applicable to a perfect gas will also be true for an irreversible process?

(a) δQ=dU+PdV

(b) δQ=TdS

(c) TdS=dU+PdV

(d) None of these

Q6. The entropy-change for any closed system which undergoes an irreversible adiabatic process

(a) may be positive, negative or zero

(b) may be positive or zero but not negative

(c) is always positive

(d) is always negative

Q7. The change in entropy of the system, 〖∆S〗_sys, undergoing a cyclic irreversible process is

(a) greater than zero

(b) equal to zero

(c) less than zero

(d) equal to the 〖∆S〗_surrounding

Q8. Consider the following statements regarding SI engine:

- Specific output is higher than CI engine.
- It can burn leaner mixtures than CI engine.
- For a given volumetric capacity, its power output is lesser than CI engine.
- Its exhaust pollution is higher relative to CI engine.

Which of the above statements is/are correct?

(a) 1, 2, 3 and 4

(b) 2 only

(c) 2, 3 and 4 only

(d) 1 and 4 only

Q9. The process of augmenting the engine power by raising the pressure of charge, fed into the engine cylinder, is called

(a) doping

(b) supercharging

(c) plunging

(d) scavenging

Q10. The power output of a supercharged engine is higher than its naturally aspirated counterpart due to the following reasons:

- The amount of inducted air is increased.
- Slight improvement in mechanical efficiency.
- Recovery of supercharger work by positive gas exchange work.
- Better scavenging and reduced exhaust gas temperature.

Which of these reasons are valid?

(a) 1, 2, 3 and 4

(b) 1,2 and 3

(c) 1, 2 and 4

(d) 2, 3 and 4

Soltions

S1. Ans.(c)

Pickering Governor is centrifugal type governor and used in gramophone.

S2. Ans.(c)

Sol. Stiffness of the spring in Hartnell governor = (S_1-S_2)/h

S3. Ans (c)

Sol. Among the given options Aluminium has the highest thermal conductivity and saturated water vapor has the lowest one.

S4. Ans (d)

Sol. Value of thermal conductivity k may be constant or vary.

S5. Ans (c)

Sol. TdS=dU+PdV

This equation consists of only point functions, so it is valid for all processes and also for perfect gas.

S6. Ans (c)

Sol. When the system is undergoing an irreversible adiabatic process.

Then, Change in entropy ∆S=∫▒dQ/T+S_gen

∫▒dQ/T=0 and ∆S>0

So, ∆S=S_gen (always positive)

S7. Ans (a)

Sol. The change in entropy of the system, 〖∆S〗_sys, undergoing a cyclic irreversible process is

〖As we know that ∆S〗_sys=∫▒dQ/T+S_gen

But for cyclic process ∫▒dQ/T=0 (because it is a point function) and S_gen is a path function.

So, 〖∆S〗_sys=S_gen (>0)

S8. Ans (d)

Sol. Specific output of an SI engine is more than that of CI engine. Specific output is the power obtained per unit of piston displacement. Keeping total piston displacement in one cycle constant, we will have same compression ratio for both the engines as volume before compression and after compression will be same for both engines. For same compression ratio, Otto cycle has more efficiency than diesel cycle. So, power for an Otto cycle will be more.

Diesel engines work in leaner ranges of fuel, so the emissions of CO and HC are supposedly lesser than in SI.

S9. Ans (b)

Sol. Supercharging is process to increase pressure of the charge or indirectly increasing the volumetric efficiency of the engine, which results in higher power in the engine.

Supercharging reduces specific fuel consumption of diesel engines (unfortunately in a small amount) for two reasons 1) energy of exhausted gases can be partially recovered 2) higher pressure inside cylinder improves fuel injection

S10. Ans (a)

Sol. All of the statements given are correct.