NEET Practice: Physics 5

1. A stone is thrown horizontally with velocity 10 m/s from a height of 20 m. The time taken to reach the ground (g=10 m/s²) is:

(a) 1 s (b) 2 s (c) 4 s (d) √2 s

Show Answer & Explanation

Correct Answer: (b) 2 s

Explanation:
Vertical motion: h = ½gt ² → 20 = 5t² → t = 2 s

2. The orbital velocity of a satellite close to Earth’s surface is:

(a) 7.9 km/s (b) 11.2 km/s (c) 3.1 km/s (d) 5.6 km/s

Show Answer & Explanation

Correct Answer: (a) 7.9 km/s

Explanation:
v₀ = √(GM/R) ≈ 7.9 km/s

3. The electric field inside a charged conductor is:

(a) Zero (b) Infinite (c) Finite and constant (d) Varies with distance

Show Answer & Explanation

Correct Answer: (a) Zero

Explanation:
In electrostatic equilibrium, E = 0 inside a conductor

4. Two wires of same material have lengths L and 2L, radii r and 2r. The ratio of their resistances is:

(a) 1:1 (b) 1:2 (c) 2:1 (d) 4:1

Show Answer & Explanation

Correct Answer: (c) 2:1

Explanation:
R ∝ L/r² → R₁/R₂ = (L/r ²) / (2L/(4r²)) = 2/1

5. The power dissipated in a resistor is maximum when:

(a) Current is maximum (b) Voltage is maximum (c) Resistance equals load (d) Frequency is zero

Show Answer & Explanation

Correct Answer: (c) Resistance equals load

Explanation:
Maximum power transfer theorem: R_load = R_internal

6. The critical angle for total internal reflection from glass to air is 42°. The refractive index of glass is:

(a) 1.5 (b) 1.414 (c) 1.33 (d) 2.0

Show Answer & Explanation

Correct Answer: (a) 1.5

Explanation:
μ = 1 / sin C ≈ 1 / sin42° ≈ 1.5

7. In an LCR series circuit at resonance, the impedance is equal to:

(a) R (b) X_L (c) X_C (d) Zero

Show Answer & Explanation

Correct Answer: (a) R

Explanation:
At resonance, X_L = X_C → Z = R

8. The number of α and β particles emitted in the decay of ²³⁸U to ²⁰⁶Pb are respectively:

(a) 8 and 6 (b) 6 and 8 (c) 4 and 8 (d) 8 and 4

Show Answer & Explanation

Correct Answer: (a) 8 and 6

Explanation:
Mass decrease 32 → 8 α particles. Atomic number decrease adjusted by 6 β particles.

9. A body of mass m is moving with velocity v. Its kinetic energy is E. If mass is doubled and velocity is halved, new kinetic energy is:

(a) E/2 (b) E (c) 2E (d) E/4

Show Answer & Explanation

Correct Answer: (a) E/2

Explanation:
New KE = (1/2)(2m)(v/2)² = (1/4)mv² = E/2

10. The mirror formula is:

(a) 1/f = 1/v + 1/u (b) 1/f = 1/v - 1/u (c) f = u + v (d) 1/v = 1/f + 1/u

Show Answer & Explanation

Correct Answer: (a) 1/f = 1/v + 1/u

Explanation:
Standard mirror formula (Cartesian sign convention)