Quiz: Mechanical Engineering

Exam: UPPSC AE

Topic: Miscellaneous

Each question carries 1 mark

Negative marking: 1/4 mark

Time: 10 Minutes

Q1. A closed system undergoes a process 1-2 for which the values of Q_(1-2) and W(1-2) are + 20kJ and + 50kJ, respectively. If the system is returned to state 1 and Q(2-1) is –10kJ, what is the value of the work W(2-1) ?

(a) +20 kJ

(b) -40 kJ

(c) -80 kJ

(d) +40 kJ

L1Difficulty 3

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Q2. The thermodynamic parameters are

1. Temperature 2. Specific volume

3. Pressure 4. Enthalpy

5. Entropy

The Clapeyron Equation of state provides relationship between:

(a) 1 and 2

(b) 2, 3 and 4

(c) 3, 4 and 5

(d) 1, 2, 3 and 4

L1Difficulty 3

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Q3. What is the pressure inside a soap bubble, over the atmospheric pressure if its diameter is 2 cm and the surface tension is 0.1 N/m?

(a) 0.4 N/m²

(b) 4.0 N/m²

(c) 40.0 N/m²

(d) 400.0 N/m²

L1Difficulty 3

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Q4. The predominant forces acting on an element of fluid in the boundary layer over a flat plate placed in a uniform stream include.

(a) inertia and pressure forces

(b) viscous and pressure forces

(c) viscous and body forces

(d) viscous and inertia forces

L1Difficulty 3

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Q5. Once-through boilers will not have

(a) Drums, headers and pumps

(b) Drums, steam separators and pumps

(c) Drums, headers and steam separators

(d) Drums, headers, steam separators and pumps

L1Difficulty 3

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Q6. Consider the following statements

The reheat cycle helps to reduce

1. Fuel consumption

2. Steam flow

3. The condenser size

Which of these statements are correct?

(a) 1 and 2

(b) 1 and 3

(c) 2 and 3

(d) 1, 2 and 3

L1Difficulty 3

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Q7. Match List-I (Parameter) with List-II (Definition) and select answer using the codes given below the lists:

List-I

A. Time constant of a thermometer of radius r0

B. Biot number for a sphere of radius r0

C. Critical thickness of insulation for a wire of radius r0

D. Nusselt number for a sphere of radius r0

List – II

1. (hr_o)/k_fluid 2. k/h

3. (hr_o)/(3k_solid ) 4. (hπr_o l)/ρCV

Nomenclature : h : film heat transfer coefficient, ksolid : thermal conductivity of solid kfluid : thermal conductivity of fluid, ρ : density, c : specific heat, V : volume, ℓ : length

codes

A B C D

(a) 4 3 2 1

(b) 1 2 3 4

(c) 2 3 4 1

(d) 4 1 2 3

L1Difficulty 3

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Q8. Which of the following factors are responsible for formation of NoX in spark ignition engine combustion:

1. Incomplete combustion

2. High temperature

3. Availability of oxygen

(a) 2 and 3

(b) 1 and 2

(c) 1 and 3

(d) 1, 2 and 3

L1Difficulty 3

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Q9. In a particular application, the shaft is subjected to bending loads and also large axial loads. The bearing suitable for supporting such a shaft is

(a) thrust bearing

(b) tapered roller bearing

(c) ball bearing

(d) spherical roller bearing

L1Difficulty 3

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Q10. In exponential smoothening method of forecasting the forecast to higher values of the smoothing constant

(a) will be more sensitive to forecast of the previous period

(b) will be more sensitive to changing patterns in demand

(c) will not be affected by the forecast of the previous period

(d) will not be affected by the changing patterns in demand

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SOLUTIONS

S1. Ans.(b)

Sol. For process 1 -2

U_1+Q=U_2+W

U_1-U_2=W-Q=50-20=30 kJ

For process 2 – 1

U_2+Q=U_1+W

Q+U_2-U_1=W

-10-30=W

W=-40 kJ

S2. Ans.(d)

Sol. The Clapeyron equation is (dp/dT)_Sat=h_fg/(T.V_fg )

It enables us to determine the enthalpy of vaporization h_fgat a given temperature by simply measuring the slope of saturation curve on a p-T diagram and the specific volume of saturated liquid and saturated vapour at given temperature.

S3. Ans.(c)

Sol.

Pressure=8σ/d=(8×0.1)/(2×10^(-2) )

=0.4×100=40 N/m²

S4. Ans.(d)

Sol. Reynolds number is used to characterize flow regimes, such as laminar flow and turbulent flow. It gives measure of the ratio of inertial force to viscous force. It consequently quantities the importance of boundary layer concept

S5. Ans.(c)

Sol. Benson boiler is a typical high pressure, dur less, water tube, forced circulated once through boiler. It has a unique characteristic of absence of drum entire process of heating, steam, continuous tube.

Feeds pumps feeds water to economizer from where it goes to radiant section

S6. Ans.(a)

Sol. Condenser size decreases due to regeneration not reheating

S7. Ans.(a)

Sol.

Biot number =(hr_0)/k_solid

Nusselt number=(hr_0)/k_fluid

Critical thickness of insulation of a wire

r_0=k/h

Time constant =ρCV/hA

Where V = volume

A = area

S8. Ans.(a)

Sol. Presence of high temperature in cylinder and availability of O2 promotes formation of NOX.

S9. Ans.(b)

Sol.

S10. Ans.(b)

Sol. Small value of smoothing coefficient (α) is selected if the demand pattern is smooth or stable and large value of α is used for fluctuating demand.