A body travels first half distance at speed v₁ and second half at v₂. Average speed is: MCQ with Answer and Explanation

A body travels first half distance at speed v₁ and second half at v₂. Average speed is:
A. √(v₁v₂)
B. (v₁+v₂)/2
C. v₁v₂/(v₁+v₂)
D. 2v₁v₂/(v₁+v₂)
Answer: Option D
Solution (By JKSSB Mock Tests)
For equal distances: average speed = total distance/total time = 2d/(d/v₁ + d/v₂) = 2v₁v₂/(v₁+v₂). This is harmonic mean, not arithmetic. Memory tip: Equal distances ⇒ harmonic mean of speeds; equal times ⇒ arithmetic mean. Frequently tested kinematics concept distinguishing average speed calculation methods.

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Correct Answer: Option A


Explanation:
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Correct Answer: Option B


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Covering part of a lens reduces the amount of light reaching the image, making it fainter, but the entire image is still formed because light from each object point can pass through the uncovered portion and converge to the corresponding image point. Image position, size, and nature remain unchanged. Memory aid: 'Partial lens coverage ⇒ reduced intensity, not partial image'. This conceptual question tests understanding of image formation principles, commonly featured in competitive exams to identify misconceptions about ray optics. Always recall that every point on lens contributes to entire image.

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Correct Answer: Option D


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