Quiz: Mechanical Engineering

Exam: USSSC JE

Topic: Miscellaneous

Each question carries 1 mark

Negative marking: 1/4 mark

Time: 10 Minutes

Q1. An ideal gas at 27°C is heated at constant pressure till its volume becomes three times. The temperature of gas then will be

(a) 81°C

(b) 900°C

(c) 627°C

(d) 927°C

L1Difficulty 3

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Q2. Work done in an adiabatic process between a given pair of end states depends on

(a) the end states only

(b) particular adiabatic process

(c) the value of index n

(d) the value of heat transferred

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Q3. Upto the critical radius of insulation

(a) convection heat loss will be less than conduction heat loss

(b) heat flux decrease

(c) added insulation will increase heat loss

(d) added insulation will decrease heat loss

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Q4. If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power will increases in the ratio of

(a) 3

(b) 9

(c) 27

(d) 81

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Q5. Match List-I with List-II and select the correct answer using the code given below the lists:

List – I

Heat exchangers

Turbulent flow

Free convection

Radiation heat transfer

List–II

View factor

Effectiveness

Nusselt number

Eddy diffusivity

Codes

A B C D

(a) 3 1 2 4

(b) 2 4 3 1

(c) 3 4 2 1

(d) 2 1 3 4

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Q6. The lowest temperature at which the oil ceases to flow cooled is known as ____________.

(a) Flash point

(b) Fire point

(c) Cloud point

(d) Pour point

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Q7. Lancashire Boiler is a

(a) Water tube boiler

(b) Fire tube boiler

(c) Locomotive boiler

(d) High pressure boiler

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Q8. Two forces act an angle of 120°. If the greater force is 50 N and their resultant is perpendicular to the smaller force, the smaller force is _________N.

(a) 20

(b) 25

(c) 30

(d) 35

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Q9. A tension member of square cross-section of side 10 mm and Young’s modulus E is to be replaced by another member of square cross-section of same length but Young’s modulus E/2. The side of the new square cross-section, required to maintain the same elongation under the same load, is nearly

(a) 14 mm

(b) 17 mm

(c) 8 mm

(d) 5 mm

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Q10. The state of stress at a point when completely specified enables one to determine the

maximum shearing stress at the point

Stress components on any arbitrary plane containing that point

Which of the above is/are correct?

(a) 1 only

(b) 2 only

(c) both 1 and 2

(d) Neither 1 nor 2

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SOLUTIONS

S1. Ans.(c)

Sol.

At constant pressure. According to Charle’s law

V α T

V_1/V_2 =T_1/T_2

T_2=(V_2/V_1 ) T_1 [V_2=3V_1 ]

= 3T1 = 3(27 + 273)

T2 = 900 K = 627°C

S2. Ans.(b)

Sol.

Work done in an adiabatic process.

W=((P_1 V_1-P_2 V_2)/(γ-1))

So, it depends on particular adiabatic process.

S3. Ans.(c)

Sol.

From the above plot between heat transfer rate versus r, it can be concluded that by providing insulation, up to critical radius heat transfer rate increase and become maximum at critical radius and further insulation decreases the heat transfer rate

S4. Ans.(d)

Sol.

T_1=273+27=300 K

T_2=627+273=900K

Emissive power = σT4

=E_2/E_1 =(T_2/T_1 )^4=(900/300)^4

E_2/E_1 =3^4=81

S5. Ans.(b)

Sol.

(a) Heat exchangers : Effectiveness

(b) Turbulent flow : Eddy diffusivity

(c) Free convection : Nusselt number

(d) Radiation heat transfer : View factor

S6. Ans.(a)

Sol.

For diesel engine, the method of governing employed is quality governing. Governing means the action of varying the fuel supply in accordance with the load demands so that the engine runs at practically constant speed. Some important methods of governing of IC engines.

1. Hit and miss governing: This method is suitable for small gas engines. In this system of governing, whenever the engine starts running at higher speed (due to decreased load), some explosions are omitted or missed. This is done with the help of a centrifugal governor.

2. Qualitative governing: In this system of governing, a control valve is fitted in the fuel delivery pipe which controls the quantity of fuel to be mixed in the charge. The movement of control valve is regulated by the centrifugal governor through rack and pinion arrangement.

3. Quantitative governing: In this system of governing, the quality of charge (i.e. air-fuel ratio of the mixture) is kept constant, but the quantity of mixture supplied to the engine cylinder is varied by means of a throttle valve which is regulated by the centrifugal governor through rack and pinion arrangement.

S7. Ans.(b)

Sol.

Lancashire Boiler is a fire tube boiler.

S8. Ans.(b)

Sol.

P_2 cos60°=P_1

P_1=50×1/2=25N

S9. Ans.(a)

Sol.

δ_I=δ_II

or,(PL/AE)_I=(PL/AE)_II

or,A_I E_I=A_II E_II

or,A_II=E_I/E_II .A_I=2×10×10=200 mm²

s^2=200 mm²

⇒s=14.14 mm

S10. Ans.(c)

Sol.

Max shear stress,

τ_max=√(((σ_x-σ_y)/2)^2+τ_xy^2 )

Normal stress on oblique plane

σ^’=(σ_x+σ_y)/2+(σ_x-σ_y)/2 cos2θ+τ_xy sin2θ

τ^’=((σ_x-σ_y)/2)sin2θ+τ_xy cos2θ