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NEET Practice: Physics 4
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1.
A force of 10 N acts on a body of mass 2 kg for 5 seconds. The change in momentum is:
(a) 10 kg m/s
(b) 20 kg m/s
(c) 50 kg m/s
(d) 100 kg m/s
Show Answer & Explanation
Correct Answer: (c) 50 kg m/s
Explanation:
Impulse = F × t = 10 × 5 = 50 kg m/s = change in momentum
2.
The kinetic energy of a body is increased by 300%. The percentage increase in momentum is:
(a) 50%
(b) 100%
(c) 141%
(d) 200%
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Correct Answer: (b) 100%
Explanation:
KE ∝ v², p ∝ v → if KE becomes 4 times, v becomes 2 times → momentum doubles (100% increase)
3.
The capacitance of a parallel plate capacitor is doubled by doubling:
(a) Area of plates
(b) Distance between plates
(c) Charge on plates
(d) Potential difference
Show Answer & Explanation
Correct Answer: (a) Area of plates
Explanation:
C = ε₀A/d → C doubles when A doubles
4.
The frequency of fundamental mode of vibration of a string is 200 Hz. The frequency of second overtone is:
(a) 200 Hz
(b) 400 Hz
(c) 600 Hz
(d) 800 Hz
Show Answer & Explanation
Correct Answer: (c) 600 Hz
Explanation:
Second overtone is 3rd harmonic → 3 × 200 = 600 Hz
5.
A body is dropped from a height h. The time taken to reach the ground is t. The time taken to fall through the last half of the distance is:
(a) t/√2
(b) t(√2 - 1)
(c) t(√2 + 1)
(d) t/2
Show Answer & Explanation
Correct Answer: (b) t(√2 - 1)
Explanation:
Time to fall h/2 = t/√2. Remaining time = t - t/√2 = t(1 - 1/√2) = t(√2 - 1)
6.
The angle of minimum deviation for a prism of refractive index √3 is 60°. The angle of prism is:
(a) 30°
(b) 45°
(c) 60°
(d) 90°
Show Answer & Explanation
Correct Answer: (c) 60°
Explanation:
δ_min = (μ - 1)A → 60° = (√3 - 1)A → A = 60°
7.
In Young's double slit experiment, the fringe width is β. If the distance between slits and screen is doubled, the new fringe width is:
(a) β/2
(b) β
(c) 2β
(d) 4β
Show Answer & Explanation
Correct Answer: (c) 2β
Explanation:
β = λD/d → D doubled → β doubled
8.
The decay constant of a radioactive substance is λ. Its half-life is:
(a) ln2 / λ
(b) λ / ln2
(c) λ / 2
(d) 2λ
Show Answer & Explanation
Correct Answer: (a) ln2 / λ
Explanation:
T_{1/2} = 0.693 / λ = ln2 / λ
9.
The work done in stretching a spring by x is W. The work done in stretching it by 2x is:
(a) W
(b) 2W
(c) 4W
(d) 8W
Show Answer & Explanation
Correct Answer: (c) 4W
Explanation:
W = (1/2)kx ² → for 2x, work = (1/2)k(2x)² = 4W
10.
The direction of induced current is given by:
(a) Fleming’s left hand rule
(b) Fleming’s right hand rule
(c) Right hand thumb rule
(d) Ampere’s swimming rule
Show Answer & Explanation
Correct Answer: (b) Fleming’s right hand rule
Explanation:
Fleming’s right hand rule is used for direction of induced current (generator rule)