NEET Practice: Physics 3

1. The velocity of sound in air is 340 m/s. The minimum distance between two reflecting surfaces for hearing an echo is:

(a) 8.5 m (b) 17 m (c) 34 m (d) 68 m

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Correct Answer: (b) 17 m

Explanation:
Minimum distance = v × t / 2 = 340 × 0.1 / 2 = 17 m (t = 0.1 s)

2. A body is projected vertically upward with velocity 20 m/s. The maximum height reached (g=10 m/s²) is:

(a) 10 m (b) 20 m (c) 30 m (d) 40 m

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Correct Answer: (b) 20 m

Explanation:
H = u ²/(2g) = 400 / 20 = 20 m

3. The unit of magnetic moment is:

(a) A m² (b) A m (c) N m / A (d) T m²

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Correct Answer: (a) A m²

Explanation:
Magnetic moment m = I × A → unit is Ampere metre square

4. Three resistors of 3 Ω, 6 Ω and 9 Ω are connected in parallel. The equivalent resistance is:

(a) 18 Ω (b) 2 Ω (c) 1.64 Ω (d) 9 Ω

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Correct Answer: (c) 1.64 Ω

Explanation:
1/R = 1/3 + 1/6 + 1/9 = 11/18 → R = 18/11 ≈ 1.64 Ω

5. The time period of a geostationary satellite is:

(a) 6 hours (b) 12 hours (c) 24 hours (d) 48 hours

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Correct Answer: (c) 24 hours

Explanation:
Geostationary satellites have orbital period equal to Earth's rotation period (24 hrs)

6. The lens maker’s formula is 1/f = (μ – 1)(1/R₁ – 1/R₂). For a plano-convex lens, R₂ = ∞. The focal length is:

(a) R/(μ–1) (b) R/(2(μ–1)) (c) (μ–1)/R (d) 2R/(μ–1)

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Correct Answer: (a) R/(μ–1)

Explanation:
1/f = (μ – 1)(1/R – 0) → f = R/(μ – 1)

7. The rms value of current I = I₀ sin(ωt) is:

(a) I₀ (b) I₀/√2 (c) I₀/2 (d) 2I₀

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Correct Answer: (b) I₀/√2

Explanation:
I_rms = I₀ / √2

8. The binding energy per nucleon is maximum for:

(a) Helium (b) Iron (c) Uranium (d) Hydrogen

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Correct Answer: (b) Iron

Explanation:
Iron (Fe-56) has the highest binding energy per nucleon

9. A body of mass 2 kg has kinetic energy 100 J. Its momentum is:

(a) 10 kg m/s (b) 20 kg m/s (c) 30 kg m/s (d) 40 kg m/s

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Correct Answer: (b) 20 kg m/s

Explanation:
KE = p²/(2m) → p = √(2m KE) = √(400) = 20 kg m/s

10. The colour of the star having highest temperature is:

(a) Red (b) Yellow (c) White (d) Blue

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Correct Answer: (d) Blue

Explanation:
Wien’s law: Higher temperature → shorter wavelength (blue)