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Topics in JEE Physics
A uniform rod of mass M and length L is pivoted at one end. The moment of inertia about the pivot is:
Correct Answer:
A. ML²/3
EXPLANATION
For a uniform rod about one end, I = ML²/3 (standard formula)
A particle experiences a force F = 2i + 3j (N) and displacement s = 4i + 6j (m). The work done is:
Correct Answer:
C. 26 J
EXPLANATION
W = F·s = (2×4) + (3×6) = 8 + 18 = 26 J
A rotating wheel has moment of inertia 2 kg·m² and angular acceleration 3 rad/s². The torque required is:
Correct Answer:
D. 6 N·m
EXPLANATION
τ = Iα = 2 × 3 = 6 N·m
A man of mass 60 kg stands on a weighing scale in an elevator moving downward with acceleration 2 m/s². The scale reading is (g = 10 m/s²):
Correct Answer:
A. 480 N
EXPLANATION
Normal force N = m(g - a) = 60(10 - 2) = 60 × 8 = 480 N
A disc of radius 0.5 m rolls without slipping on a horizontal surface with angular velocity 4 rad/s. The velocity of the center of mass is:
Correct Answer:
B. 2 m/s
EXPLANATION
For rolling without slipping, v = ωr = 4 × 0.5 = 2 m/s
A force of 10 N acts on a mass for 5 seconds, changing its momentum by:
Correct Answer:
C. 50 kg·m/s
EXPLANATION
By impulse-momentum theorem, Δp = F·Δt = 10 × 5 = 50 kg·m/s
A projectile is launched at 45° with initial velocity 20 m/s. Taking g = 10 m/s², the range is:
Correct Answer:
B. 40 m
EXPLANATION
Range = u²sin(2θ)/g = (400 × sin(90°))/10 = 400/10 = 40 m
A stone is dropped from height h. If air resistance is ignored, what fraction of its total energy is kinetic at height h/2?
Correct Answer:
B. 1/2
EXPLANATION
At h/2, PE = mg(h/2), Total energy = mgh. KE = mgh - mg(h/2) = mg(h/2). Fraction = (h/2)/h = 1/2
Two objects of equal mass collide elastically and exchange velocities. This is possible only if:
Correct Answer:
A. One object was at rest before collision
EXPLANATION
In elastic collision between equal masses, if one is at rest, they exchange velocities completely. This satisfies both momentum and energy conservation.
The coefficient of static friction between a block and surface is 0.5. The maximum angle of incline at which the block remains stationary is approximately:
Correct Answer:
A. 26.6°
EXPLANATION
At maximum angle, tan(θ) = μs = 0.5, so θ = tan⁻¹(0.5) ≈ 26.6°
