The weight of a body at Earth's centre is MCQ with Answer and Explanation
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Question #1
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Assertion (A): The coefficient of kinetic friction is always strictly less than the coefficient of limiting static friction. Reason (R): Once motion starts, the inertia of rest is broken and interlocking of surface irregularities is less effective.
Correct Answer: Option D
Explanation:
Static friction opposes impending motion, reaching a maximum called limiting friction. Once the object moves, it doesn't have enough time for the microscopic irregularities (asperities) of the two surfaces to interlock strongly. Thus, the force required to keep it moving (kinetic friction) is slightly less than the force required to start the motion.
Static friction opposes impending motion, reaching a maximum called limiting friction. Once the object moves, it doesn't have enough time for the microscopic irregularities (asperities) of the two surfaces to interlock strongly. Thus, the force required to keep it moving (kinetic friction) is slightly less than the force required to start the motion.
Question #2
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Assertion (A): In a purely resistive AC circuit, voltage and current are in phase. Reason (R): Resistors do not store energy; they dissipate it as heat.
Correct Answer: Option C
Explanation:
Assertion is true: in resistive AC circuits, V and I reach peaks simultaneously (phase difference 0°). Reason is true and explains A: resistors obey Ohm's law instantaneously (V=IR), with no energy storage mechanism (unlike capacitors/inductors that cause phase shifts via energy storage/release). Thus, no phase difference arises. Memory aid: 'Resistors: V and I in phase; Capacitors: I leads V; Inductors: V leads I'. This assertion-reason question tests AC circuit fundamentals, frequently examined. Always link phase behavior to energy storage properties of components.
Assertion is true: in resistive AC circuits, V and I reach peaks simultaneously (phase difference 0°). Reason is true and explains A: resistors obey Ohm's law instantaneously (V=IR), with no energy storage mechanism (unlike capacitors/inductors that cause phase shifts via energy storage/release). Thus, no phase difference arises. Memory aid: 'Resistors: V and I in phase; Capacitors: I leads V; Inductors: V leads I'. This assertion-reason question tests AC circuit fundamentals, frequently examined. Always link phase behavior to energy storage properties of components.
Question #3
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Which of the following is a vector quantity?
Correct Answer: Option B
Explanation:
Magnetic field intensity (H) and magnetic field (B) are vectors. Magnetic flux is scalar (Φ = B·A). Resistance scalar, potential scalar. Vector quantities have direction. Current has direction but adds by scalar law, considered tensor sometimes but in basic physics not vector.
Magnetic field intensity (H) and magnetic field (B) are vectors. Magnetic flux is scalar (Φ = B·A). Resistance scalar, potential scalar. Vector quantities have direction. Current has direction but adds by scalar law, considered tensor sometimes but in basic physics not vector.
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