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JEE Physics

Physics questions for JEE Main — Mechanics, Electrostatics, Optics, Modern Physics.

434 Q 9 Topics Take Test
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Difficulty: All Easy Medium Hard 381–390 of 434
Topics in JEE Physics
Q.381 Medium Thermodynamics
In an isobaric process, 5 moles of a monoatomic ideal gas are heated from 300 K to 400 K. What is the heat supplied? (R = 8.314 J/(mol·K))
A Q = 20.785 kJ
B Q = 41.57 kJ
C Q = 62.355 kJ
D Q = 31.178 kJ
Correct Answer:  C. Q = 62.355 kJ
EXPLANATION

For isobaric process: Q = nCₚΔT. For monoatomic gas, Cₚ = (5/2)R. Q = 5 × (5/2) × 8.314 × 100 = 62.355 kJ

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Q.382 Medium Thermodynamics
A cyclic process consists of two isothermal and two adiabatic processes (Carnot cycle). What is true about the heat exchanges?
A Heat is exchanged in both isothermal processes only
B Heat is exchanged in adiabatic processes
C Net heat exchange is always zero
D Heat exchange is equal in both isothermal processes
Correct Answer:  A. Heat is exchanged in both isothermal processes only
EXPLANATION

In Carnot cycle, isothermal processes involve heat exchange with reservoirs (Q₁ at hot reservoir, Q₂ at cold reservoir), while adiabatic processes have no heat exchange (Q=0)

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Q.383 Medium Thermodynamics
In an adiabatic process with a diatomic ideal gas (γ = 1.4), if the initial temperature is 300 K and volume increases by factor of 2, what is the final temperature?
A T₂ = 178.9 K
B T₂ = 212.1 K
C T₂ = 195.7 K
D T₂ = 223.4 K
Correct Answer:  A. T₂ = 178.9 K
EXPLANATION

For adiabatic process: TVγ⁻¹ = constant. T₁V₁^(γ-1) = T₂V₂^(γ-1). 300 × 1^0.4 = T₂ × 2^0.4. T₂ = 300/2^0.4 = 300/1.6818 = 178.9 K

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Q.384 Medium Thermodynamics
A gas undergoes an isothermal process at 300 K. If the initial volume is 2 L and final volume is 5 L, what is the work done by the gas? (Take R = 8.314 J/(mol·K), n = 1 mol)
A W = 2.74 kJ
B W = 3.04 kJ
C W = 2.50 kJ
D W = 1.98 kJ
Correct Answer:  B. W = 3.04 kJ
EXPLANATION

For isothermal process: W = nRT ln(Vf/Vi) = 1 × 8.314 × 300 × ln(5/2) = 2494.2 × 1.609 = 3.04 kJ

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Q.385 Medium Mechanics
A particle of mass m undergoes motion with velocity v(t) = 3t² + 2t (in m/s). What is the net force on the particle when t = 2 s, if m = 2 kg?
A 28 N
B 16 N
C 32 N
D 24 N
Correct Answer:  A. 28 N
EXPLANATION

Acceleration a = dv/dt = 6t + 2. At t=2s: a = 6(2) + 2 = 14 m/s². Force F = ma = 2 × 14 = 28 N

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Q.386 Medium Mechanics
Two blocks A (mass 3 kg) and B (mass 2 kg) are connected by a light string over a frictionless pulley. Block A is on a smooth horizontal surface and B hangs vertically. What is the acceleration of the system? (g = 10 m/s²)
A 4 m/s²
B 2 m/s²
C 3 m/s²
D 5 m/s²
Correct Answer:  A. 4 m/s²
EXPLANATION

For Atwood-like system with one block horizontal: a = (m_B × g)/(m_A + m_B) = (2 × 10)/(3 + 2) = 20/5 = 4 m/s²

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Q.387 Medium Mechanics
A ball is thrown vertically upward with velocity 30 m/s. At what time does it return to the ground level? (g = 10 m/s²)
A 3 s
B 6 s
C 4 s
D 2 s
Correct Answer:  B. 6 s
EXPLANATION

Using s = ut + ½gt² for complete journey (s=0): 0 = 30t - 5t². Solving: t(30 - 5t) = 0, giving t = 6 s (non-zero solution)

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Q.388 Medium Mechanics
A 6 kg object is subject to two perpendicular forces: F₁ = 8 N and F₂ = 6 N. What is the magnitude of acceleration?
A 1.5 m/s²
B 1.67 m/s²
C 2.33 m/s²
D 3 m/s²
Correct Answer:  B. 1.67 m/s²
EXPLANATION

Resultant force = √(8² + 6²) = √(64 + 36) = √100 = 10 N. Acceleration = F/m = 10/6 = 1.67 m/s²

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Q.389 Medium Mechanics
A 4 kg block on a rough horizontal surface experiences friction force f = 12 N when moving. If pushed with force 20 N, what is the kinetic energy after traveling 5 m from rest?
A 20 J
B 40 J
C 60 J
D 80 J
Correct Answer:  B. 40 J
EXPLANATION

Net force = 20 - 12 = 8 N. Work done by net force = 8 × 5 = 40 J. This equals KE gained = 40 J

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Q.390 Medium Mechanics
A rectangular block of dimensions 10 cm × 20 cm × 30 cm is floating in water. Which orientation is most stable?
A 10×20 cm face down
B 10×30 cm face down
C 20×30 cm face down
D All are equally stable
Correct Answer:  C. 20×30 cm face down
EXPLANATION

Stability increases with larger base area and lower center of gravity. The 20×30 cm face down provides the largest base area, ensuring maximum stability.

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