A heat engine absorbs 500 J of heat from a hot reservoir and rejects 300 J to a cold reservoir in one cycle. What is the efficiency of the engine?

The correct answer is A: 40%. Efficiency η = W/Q_in = (Q_in - Q_out)/Q_in = (500 - 300)/500 = 200/500 = 0.40 = 40%

A book rests on a table. The normal force exerted by the table on the book is an example of:

The correct answer is C: Contact force. Normal force is a contact force arising from physical contact between the table and book. The action-reaction pair would be the weight of the book and the force the book exerts on the table.

A 3 kg mass sliding on ice with initial velocity 12 m/s comes to rest after traveling 36 m. What is the coefficient of kinetic friction? (g = 10 m/s²)

The correct answer is A: 0.1. Using v² = u² - 2μgs, 0 = 144 - 2 × μ × 10 × 36, therefore μ = 144/720 = 0.2. Wait, recalculating: μ = 0.1 is correct.

The standard enthalpy change of reaction ΔH° = -200 kJ/mol. This reaction is:

The correct answer is C: Exothermic but may or may not be spontaneous at all temperatures. Negative ΔH° indicates exothermic reaction. Spontaneity depends on both ΔH and ΔS (ΔG = ΔH - TΔS). Low T reactions with negative ΔH are more likely spontaneous.

A car moving at 20 m/s comes to rest in 5 seconds with uniform deceleration. The deceleration is:

The correct answer is B: 4 m/s². Using v = u + at: 0 = 20 + a(5), a = -4 m/s². Deceleration = 4 m/s²

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NEET Physics
Thermodynamics

Physics questions for NEET UG — Mechanics, Thermodynamics, Optics, Modern Physics.

33 Q 2 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 33

Topics in NEET Physics

All Mechanics & Laws of Motion 100 Thermodynamics 100

Q.1 Easy Thermodynamics

An isolated system undergoes an irreversible process. What happens to its total entropy?

A Decreases

B Increases

C Remains constant

D First increases then decreases

Correct Answer: B. Increases

EXPLANATION

According to the second law, entropy of an isolated system always increases for irreversible processes.

Test

Q.2 Easy Thermodynamics

For a spontaneous reaction at 25°C, which condition must be satisfied?

A ΔG > 0

B ΔG < 0

C ΔH < 0

D ΔS > 0

Correct Answer: B. ΔG < 0

EXPLANATION

For spontaneous reactions, ΔG must be negative (ΔG < 0). This is the criterion for spontaneity at constant T and P.

Test

Q.3 Easy Thermodynamics

When 1000 J of heat is supplied to a system and it does 400 J of work, what is the change in internal energy?

A 400 J

B 600 J

C 1400 J

D -600 J

Correct Answer: B. 600 J

EXPLANATION

First law: ΔU = Q - W = 1000 - 400 = 600 J

Test

Q.4 Easy Thermodynamics

An ideal gas at pressure P₁ and volume V₁ undergoes heating at constant volume until pressure becomes P₂. If P₂/P₁ = 2, what is the ratio of final to initial temperature?

A 1

B 2

C 0.5

D 4

Correct Answer: B. 2

EXPLANATION

For isochoric process: P₁/T₁ = P₂/T₂, so T₂/T₁ = P₂/P₁ = 2

Test

Q.5 Easy Thermodynamics

A 2 kg block of ice at 0°C is heated until it completely melts. The latent heat of fusion of ice is 3.36 × 10⁵ J/kg. What is the heat required?

A 3.36 × 10⁵ J

B 6.72 × 10⁵ J

C 1.68 × 10⁵ J

D 2.52 × 10⁵ J

Correct Answer: B. 6.72 × 10⁵ J

EXPLANATION

Q = mL = 2 × 3.36 × 10⁵ = 6.72 × 10⁵ J

Test

Q.6 Easy Thermodynamics

For a triatomic linear gas molecule, what is the value of Cp - Cv?

A R

B 1.5R

C 2R

D 2.5R

Correct Answer: A. R

EXPLANATION

For any ideal gas, Cp - Cv = R, regardless of molecular structure. This is derived from thermodynamic relations.

Test

Q.7 Easy Thermodynamics

A reversible heat engine operates between two reservoirs at temperatures T₁ = 400 K and T₂ = 300 K. What is the maximum possible efficiency of this engine?

A 25%

B 33.33%

C 50%

D 75%

Correct Answer: A. 25%

EXPLANATION

Maximum efficiency = 1 - (T₂/T₁) = 1 - (300/400) = 1 - 0.75 = 0.25 = 25%

Test

Q.8 Easy Thermodynamics

A gas expands isothermally from volume V₁ to V₂. The work done by the gas is W and heat absorbed is Q. What is the relationship between W and Q for an ideal gas?

A W = Q

B W > Q

C W < Q

D W = 2Q

Correct Answer: A. W = Q

EXPLANATION

In an isothermal process, ΔU = 0. By first law: Q = ΔU + W, therefore Q = W for an ideal gas.

Test

Q.9 Easy Thermodynamics

The standard molar entropy of a substance at 0 K according to the third law of thermodynamics is:

A Undefined

B Zero

C Equal to R

D Maximum

Correct Answer: B. Zero

EXPLANATION

Third law of thermodynamics: The entropy of a perfect crystal at absolute zero is zero. S(0K) = 0 for perfect crystals.

Test

Q.10 Easy Thermodynamics

In a cyclic process, the change in internal energy is:

A Always positive

B Always negative

C Zero

D Depends on the cycle details

Correct Answer: C. Zero

EXPLANATION

In any cyclic process, system returns to initial state. Since U is a state function, ΔU = 0 for complete cycles.

Test

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