Archimedes' principle is used in MCQ with Answer and Explanation
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Question #1
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A car travels from point A to B with speed 40 km/h and returns from B to A with speed 60 km/h. The average speed for the entire journey is:
Correct Answer: Option C
Explanation:
Average speed = Total distance / Total time. Let distance AB = d km. Time for AB = d/40 h, time for BA = d/60 h. Total distance = 2d km. Total time = d/40 + d/60 = d(3+2)/120 = 5d/120 = d/24 h. Average speed = 2d / (d/24) = 48 km/h. Note: Average speed is not arithmetic mean of speeds (which would be 50 km/h) because time intervals differ. This harmonic mean concept is crucial for motion problems. Exam tip: For equal distances, average speed = 2v₁v₂/(v₁+v₂). Frequently tested in competitive exams.
Average speed = Total distance / Total time. Let distance AB = d km. Time for AB = d/40 h, time for BA = d/60 h. Total distance = 2d km. Total time = d/40 + d/60 = d(3+2)/120 = 5d/120 = d/24 h. Average speed = 2d / (d/24) = 48 km/h. Note: Average speed is not arithmetic mean of speeds (which would be 50 km/h) because time intervals differ. This harmonic mean concept is crucial for motion problems. Exam tip: For equal distances, average speed = 2v₁v₂/(v₁+v₂). Frequently tested in competitive exams.
Question #2
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A real image can be obtained on a screen. Which of the following always forms a virtual image?
Question #3
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The working of an electric motor is based on
Correct Answer: Option B
Explanation:
Motor converts electrical to mechanical energy using force on a current-carrying conductor in magnetic field (F = BIL). Electromagnetic induction is for generator. Motor principle: A current-carrying coil experiences torque in magnetic field.
Motor converts electrical to mechanical energy using force on a current-carrying conductor in magnetic field (F = BIL). Electromagnetic induction is for generator. Motor principle: A current-carrying coil experiences torque in magnetic field.
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