Physics is where JEE ranks are usually won or lost, since a single conceptual slip changes the whole answer. Questions here span mechanics, rotational motion, thermodynamics, waves and oscillations, electrostatics, current electricity, magnetism, optics, and modern physics. Numerical problems carry full derivations so you can see which step you skipped, not just which option was right.
A rectangular block of dimensions 10 cm × 20 cm × 30 cm is floating in water. Which orientation is most stable?
Answer: C
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.
Q.42Medium
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?
Answer: B
Net force = 20 - 12 = 8 N. Work done by net force = 8 × 5 = 40 J. This equals KE gained = 40 J
Q.43Medium
A 6 kg object is subject to two perpendicular forces: F₁ = 8 N and F₂ = 6 N. What is the magnitude of acceleration?
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)
Answer: B
Using s = ut + ½gt² for complete journey (s=0): 0 = 30t - 5t². Solving: t(30 - 5t) = 0, giving t = 6 s (non-zero solution)
Q.45Medium
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)
Answer: A
For Atwood-like system with one block horizontal: a = (m_B × g)/(m_A + m_B) = (2 × 10)/(3 + 2) = 520 = 4 m/s²
Q.46Medium
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?
Answer: A
Acceleration a = dv/dt = 6t + 2. At t=2s: a = 6(2) + 2 = 14 m/s². Force F = ma = 2 × 14 = 28 N
Q.47Medium
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)
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 cyclic process consists of two isothermal and two adiabatic processes (Carnot cycle). What is true about the heat exchanges?
Answer: A
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)
Q.50Medium
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))
For a van der Waals gas, which statement is correct?
Answer: A
Van der Waals equation (P + a/V²)(V - b) = RT accounts for molecular volume (b term) and intermolecular attractive forces (a term)
Q.55Medium
In an expansion process, a gas does 500 J of work and absorbs 300 J of heat. What is the change in internal energy?
Answer: A
Using first law: ΔU = Q - W = 300 - 500 = -200 J (internal energy decreases)
Q.56Medium
During an isobaric expansion of an ideal gas, the work done by the gas is 400 J. If pressure is constant at 2 atm, what is the change in volume? (1 atm = 101325 Pa)
Answer: B
W = PΔV. Here W = 400 J, P = 2 × 101325 = 202650 Pa. So ΔV = W/P = 202650400 ≈ 0.00197 m³
Q.57Medium
For a diatomic ideal gas undergoing an isothermal process, which quantity remains constant?
Answer: C
In an isothermal process, temperature is constant. For an ideal gas, internal energy depends only on temperature, so ΔU = 0. Pressure and volume change according to PV = constant.
Q.58Medium
Two samples of the same ideal gas at the same temperature have volumes V and 2V respectively. The ratio of their internal energies is:
Answer: D
Internal energy U = nCvT. Without knowing the number of moles in each sample, the ratio cannot be determined. Same temperature doesn't mean same internal energy.
Q.59Medium
A heat engine absorbs 1000 J of heat and rejects 600 J to the cold reservoir in one cycle. What is its efficiency?
