A SONAR signal sent from a ship returns after 2 s. If speed of sound in water is 1500 m/s, depth of sea is MCQ with Answer and Explanation
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Question #1
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Light emitting diodes (LEDs) are preferred over incandescent bulbs primarily because:
Correct Answer: Option D
Explanation:
Incandescent bulbs work by heating a tungsten filament until it glows, converting roughly 90% of electrical energy into wasted heat and only 10% into light. LEDs are solid-state semiconductors that emit light through electroluminescence. They convert almost all their electrical energy directly into light, making them significantly more efficient and cooler.
Incandescent bulbs work by heating a tungsten filament until it glows, converting roughly 90% of electrical energy into wasted heat and only 10% into light. LEDs are solid-state semiconductors that emit light through electroluminescence. They convert almost all their electrical energy directly into light, making them significantly more efficient and cooler.
Question #2
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The formula for kinetic energy is
Question #3
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The escape velocity from Earth's surface is approximately 11.2 km/s. If a planet has twice Earth's radius and same density, its escape velocity will be:
Correct Answer: Option C
Explanation:
Escape velocity v_e = √(2GM/R). Mass M = density ρ × volume = ρ×(4/3)πR³. Thus v_e = √(2Gρ×4/3πR³ / R) = √(8GρπR²/3) ∝ R√ρ. Given same density and R_planet = 2R_earth, v_e ∝ R, so v_e_planet = 2 × 11.2 = 22.4 km/s. This derivation shows escape velocity scales linearly with radius for constant density. Memory tip: v_e ∝ √(M/R) and M ∝ R³ for constant ρ, so v_e ∝ R. Such proportional reasoning questions test conceptual grasp of gravitation formulas in competitive exams without heavy calculation.
Escape velocity v_e = √(2GM/R). Mass M = density ρ × volume = ρ×(4/3)πR³. Thus v_e = √(2Gρ×4/3πR³ / R) = √(8GρπR²/3) ∝ R√ρ. Given same density and R_planet = 2R_earth, v_e ∝ R, so v_e_planet = 2 × 11.2 = 22.4 km/s. This derivation shows escape velocity scales linearly with radius for constant density. Memory tip: v_e ∝ √(M/R) and M ∝ R³ for constant ρ, so v_e ∝ R. Such proportional reasoning questions test conceptual grasp of gravitation formulas in competitive exams without heavy calculation.
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