भौतिक विज्ञान (Physics) – Physics MCQ
भौतिक विज्ञान (Physics) – इन्जिनियरिङ प्रवेश
Physics · Engineering Entrance – Mathematics, Physics, Chemistry & English · १,३९८ प्रश्न
१,३९८ प्रश्न उपलब्ध। मोड छान्नुहोस्:
भौतिक विज्ञान (Physics): प्रश्न र उत्तर
सही लागेको विकल्पमा थिच्नुहोस्। सही भए हरियो, गलत भए रातो देखिन्छ; ३ सेकेन्डपछि सही उत्तर र व्याख्या देखिन्छ।
सही: ० / ०
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A particle in SHM starts from an extreme position. The minimum time it takes to reach a displacement of half the amplitude (on the same side) is:
सही उत्तर: ख) T/6
x = A cos ωt; A/2 = A cos ωt gives ωt = π/3, so t = (π/3)/(2π/T) = T/6.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Neglecting the Earth's rotation, the minimum energy needed to put a satellite of mass m into a circular orbit at a height R above the Earth's surface (R = Earth's radius, g = surface value) is:
सही उत्तर: घ) 3mgR/4
Initial energy on the surface = −GMm/R; total energy in an orbit of radius 2R = −GMm/(4R). Energy needed = 3GMm/(4R) = 3mgR/4 (using GM = gR²).
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A satellite moves in a circular orbit close to the Earth. By what percentage must its speed be increased for it to escape from the Earth's gravity?
सही उत्तर: क) about 41.4%
Escape speed = √2 × orbital speed at the same distance, so the speed must increase by (√2 − 1) × 100% ≈ 41.4%.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Two satellites of equal mass move in circular orbits of radii r and 2r around the Earth. The ratio of their kinetic energies is:
सही उत्तर: ग) 2 : 1
For a circular orbit KE = GMm/(2r), so KE ∝ 1/r and the ratio is 2r : r = 2 : 1.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A planet moves in an elliptical orbit around the Sun. Its distances from the Sun at perihelion and aphelion are r₁ and r₂. The ratio of its speeds there, v₁ : v₂, is:
सही उत्तर: क) r₂ : r₁
Angular momentum is conserved and at these points velocity is perpendicular to the radius: m v₁ r₁ = m v₂ r₂, so v₁ : v₂ = r₂ : r₁.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A ring and a disc of the same mass and radius roll without slipping with the same linear speed. The ratio of their total kinetic energies (ring : disc) is:
सही उत्तर: घ) 4 : 3
Ring: KE = ½mv² + ½mv² = mv²; disc: KE = ½mv² + ¼mv² = ¾mv²; ratio = 1 : ¾ = 4 : 3.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The angular speed of the hour hand of a clock is about:
सही उत्तर: ख) 1.45 × 10⁻⁴ rad/s
The hour hand turns 2π rad in 12 h = 43200 s, so ω = 2π/43200 ≈ 1.45 × 10⁻⁴ rad/s.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The moment of inertia of a uniform disc of mass M and radius R about a tangent perpendicular to its plane is:
सही उत्तर: ग) 3MR²/2
By the parallel axes theorem, I = MR²/2 + MR² = 3MR²/2.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The moment of inertia of a thin uniform ring of mass M and radius R about any diameter is:
सही उत्तर: घ) MR²/2
By the perpendicular axes theorem, I_x + I_y = I_z = MR² and by symmetry I_x = I_y, so I(diameter) = MR²/2.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Springs A and B have force constants 100 N/m and 200 N/m. When each is stretched by the same force, the ratio of the energies stored, E_A : E_B, is:
सही उत्तर: ख) 2 : 1
With the same force F, x = F/k and E = F²/(2k), so E ∝ 1/k: E_A : E_B = 200 : 100 = 2 : 1.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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