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English SSC CGL Tier I papers. Free 60-minute mocks, 100 questions, 200 marks; +2 correct and −0.5 incorrect. Source: SSC response sheets preserved by SSC Portal. The marked archived keys have not been independently revalidated against final SSC keys; worked explanations are pending review. A/B/C/D correspond to source options 1/2/3/4.

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Question 1 · Mechanical Engineering (SSC JE) · Heat Transfer
Fourier’s law of heat conduction states that the heat flux is proportional to
Choose your answer for question 1
Answer and explanation

Correct answer: B

q = −k dT/dx, with the negative sign showing that heat flows from hot to cold.

Question 2 · Mechanical Engineering (SSC JE) · Heat Transfer
A plane wall has a thermal conductivity of 0.5 W/m·K and a thickness of 0.2 m. The temperature difference across it is 40 °C. The heat flux is
Choose your answer for question 2
Answer and explanation

Correct answer: B

q = k ΔT / L = 0.5 × 40 / 0.2 = 100 W/m².

Question 3 · Mechanical Engineering (SSC JE) · Heat Transfer
According to the Stefan-Boltzmann law, if the absolute temperature of a black body is doubled, the emissive power increases by a factor of
Choose your answer for question 3
Answer and explanation

Correct answer: D

E = σT⁴, so doubling T gives 2⁴ = 16 times the emissive power.

Question 4 · Mechanical Engineering (SSC JE) · Heat Transfer
The Nusselt number is defined as
Choose your answer for question 4
Answer and explanation

Correct answer: A

It is the ratio of convective to conductive heat transfer across a boundary.

Question 5 · Mechanical Engineering (SSC JE) · Heat Transfer
Fins are provided on a surface to
Choose your answer for question 5
Answer and explanation

Correct answer: C

More surface area to the fluid helps when the heat transfer coefficient is low, as with air.

Question 6 · Mechanical Engineering (SSC JE) · Heat Transfer
The critical radius of insulation for a cylinder is given by
Choose your answer for question 6
Answer and explanation

Correct answer: D

Insulation below this radius increases the heat loss, because the outer area grows faster than the resistance of the insulation.

Question 7 · Mechanical Engineering (SSC JE) · Heat Transfer
A composite wall has two layers: k1 = 1 W/m·K, thickness 0.1 m, and k2 = 0.5 W/m·K, thickness 0.1 m. The temperature difference across the wall is 60 °C. The heat flux is
Choose your answer for question 7
Answer and explanation

Correct answer: B

R = 0.1/1 + 0.1/0.5 = 0.3 m²K/W. q = ΔT/R = 60/0.3 = 200 W/m².

Question 8 · Mechanical Engineering (SSC JE) · Heat Transfer
In a counterflow heat exchanger, hot fluid cools from 100 °C to 60 °C and cold fluid heats from 30 °C to 50 °C. The LMTD is about
Choose your answer for question 8
Answer and explanation

Correct answer: D

ΔT1 = 100 − 50 = 50 °C and ΔT2 = 60 − 30 = 30 °C. LMTD = (50 − 30)/ln(50/30) = 20/0.511 = 39.2 °C.

Question 9 · Mechanical Engineering (SSC JE) · Heat Transfer
A lumped capacitance analysis of transient conduction is valid when the Biot number is
Choose your answer for question 9
Answer and explanation

Correct answer: A

Bi = hL/k < 0.1 means that the internal resistance of the solid is small, so its temperature is nearly uniform.

Question 10 · Mechanical Engineering (SSC JE) · Heat Transfer
In the effectiveness-NTU method of heat exchanger analysis, NTU is defined as
Choose your answer for question 10
Answer and explanation

Correct answer: A

NTU is the number of transfer units, the ratio of the thermal size UA to the smaller heat capacity rate.

Question 11 · Mechanical Engineering (SSC JE) · Heat Transfer
The Prandtl number is defined as
Choose your answer for question 11
Answer and explanation

Correct answer: B

It is the ratio of momentum diffusivity to thermal diffusivity.

Question 12 · Mechanical Engineering (SSC JE) · Heat Transfer
According to Wien’s displacement law, the peak emission of a black body at 1449 K occurs at a wavelength of about (λmax·T = 2898 μm·K)
Choose your answer for question 12
Answer and explanation

Correct answer: A

λmax = 2898 / 1449 = 2 μm.

Question 13 · Mechanical Engineering (SSC JE) · Heat Transfer
A surface of area 5 m² at a temperature 50 °C above that of the surrounding fluid loses heat by convection with h = 10 W/m²·K. The rate of heat transfer is
Choose your answer for question 13
Answer and explanation

Correct answer: C

Q = hAΔT = 10 × 5 × 50 = 2500 W.

Question 14 · Mechanical Engineering (SSC JE) · Heat Transfer
By Wien’s displacement law (λmax T = 2898 μm·K), the wavelength of maximum emission of a black body at 2740 K is
Choose your answer for question 14
Answer and explanation

Correct answer: A

λmax = 2898/2740 = 1.06 μm.

Question 15 · Mechanical Engineering (SSC JE) · Heat Transfer
By Wien’s displacement law (λmax T = 2898 μm·K), the wavelength of maximum emission of a black body at 1760 K is
Choose your answer for question 15
Answer and explanation

Correct answer: A

λmax = 2898/1760 = 1.65 μm.

Question 16 · Mechanical Engineering (SSC JE) · Heat Transfer
The emissive power of a black body at 1500 K (σ = 5.67 × 10⁻⁸ W/m²K⁴) is
Choose your answer for question 16
Answer and explanation

Correct answer: B

E = σT⁴ = 5.67×10⁻⁸ × 1500⁴ = 287044 W/m².

Question 17 · Mechanical Engineering (SSC JE) · Heat Transfer
A plane wall of thermal conductivity 0.5 W/m·K and thickness 0.2 m has a temperature difference of 100 °C across it. The heat flux through it is
Choose your answer for question 17
Answer and explanation

Correct answer: A

q = kΔT/L = 0.5 × 100 / 0.2 = 250 W/m².

Question 18 · Mechanical Engineering (SSC JE) · Heat Transfer
A surface of area 2 m² at a temperature 20 °C above that of the surrounding fluid loses heat by convection with h = 25 W/m²·K. The rate of heat transfer is
Choose your answer for question 18
Answer and explanation

Correct answer: D

Q = hAΔT = 25 × 2 × 20 = 1000 W.

Question 19 · Mechanical Engineering (SSC JE) · Heat Transfer
A heat exchanger has an overall heat transfer coefficient of 300 W/m²·K, an area of 2 m² and a log mean temperature difference of 30 °C. The heat transfer rate is
Choose your answer for question 19
Answer and explanation

Correct answer: D

Q = U A ΔTlm = 300 × 2 × 30 = 18000 W = 18 kW.

Question 20 · Mechanical Engineering (SSC JE) · Heat Transfer
A heat exchanger has an overall heat transfer coefficient of 300 W/m²·K, an area of 10 m² and a log mean temperature difference of 20 °C. The heat transfer rate is
Choose your answer for question 20
Answer and explanation

Correct answer: C

Q = U A ΔTlm = 300 × 10 × 20 = 60000 W = 60 kW.

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