NEET Practice: Physics 2

1. A car moving at 20 m/s is brought to rest in 4 seconds by applying brakes. The retardation produced is:

(a) 2 m/s² (b) 4 m/s² (c) 5 m/s² (d) 8 m/s²

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Correct Answer: (c) 5 m/s²

Explanation:
a = (v - u)/t = (0 - 20)/4 = -5 m/s² (retardation = 5 m/s²)

2. The escape velocity from the surface of Earth is approximately:

(a) 7.9 km/s (b) 11.2 km/s (c) 9.8 km/s (d) 5.6 km/s

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Correct Answer: (b) 11.2 km/s

Explanation:
v_esc = √(2GM/R) ≈ 11.2 km/s for Earth

3. The SI unit of electric flux is:

(a) N m²/C (b) N/C (c) V m (d) C/N

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Correct Answer: (a) N m ²/C

Explanation:
Electric flux Φ = E · A → unit is N m²/C or V m

4. A 100 W bulb is connected to 220 V mains. The resistance of the filament is:

(a) 242 Ω (b) 484 Ω (c) 220 Ω (d) 100 Ω

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Correct Answer: (b) 484 Ω

Explanation:
R = V²/P = (220)² / 100 = 484 Ω

5. The moment of inertia of a thin ring about its diameter is:

(a) MR² (b) (1/2)MR² (c) (1/4)MR² (d) 2MR²

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Correct Answer: (b) (1/2)MR²

Explanation:
By perpendicular axis theorem: I_z = I_x + I_y → I_diameter = (1/2)MR²

6. The refractive index of glass with respect to air is 1.5. Critical angle for glass-air interface is:

(a) 30° (b) 41.8° (c) 48.6° (d) 60°

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Correct Answer: (b) 41.8°

Explanation:
sin C = 1/μ = 1/1.5 ≈ 0.666 → C ≈ 41.8°

7. In an AC circuit, the voltage and current are given by V = 100 sin(100t) and I = 100 sin(100t + π/3). The power factor is:

(a) 0.5 (b) 0 (c) 1 (d) 0.866

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Correct Answer: (a) 0.5

Explanation:
Phase difference φ = π/3 → cosφ = cos(60°) = 0.5

8. The half-life of a radioactive substance is 4 days. The time taken for 7/8th of the substance to decay is:

(a) 8 days (b) 12 days (c) 16 days (d) 24 days

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Correct Answer: (b) 12 days

Explanation:
7/8 decayed means 1/8 remains → 3 half-lives = 3 × 4 = 12 days

9. The gravitational potential energy of a body of mass m at height h (h << R) is approximately:

(a) mgh (b) -GMm/R (c) -GMm/(R+h) (d) Zero

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Correct Answer: (a) mgh

Explanation:
Near surface approximation: U = mgh

10. A charged particle moves in a uniform magnetic field perpendicular to velocity. The path followed is:

(a) Straight line (b) Parabola (c) Circle (d) Helix

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Correct Answer: (c) Circle

Explanation:
Magnetic force provides centripetal force → circular path