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Question 30627
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Circular Motion: Minimum Speed at Top — Rod vs String MCQ

Solve this quality-checked JEE multiple-choice question, then review the correct answer and explanation.

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Minimum Speed at Top — Rod vs StringHardQuestion 30627

Question

For a ball on a rod (vs. string) in a vertical circle, the minimum speed at the top for maintaining circular motion is:
  1. A
    Same: √(gr)
  2. B
    For rod: 0 (rod can push); for string: √(gr) (string can only pull)
    Correct
  3. C
    For rod: √(2gr); for string: 0
  4. D
    Both require √(5gr) at bottom

Correct answer

For rod: 0 (rod can push); for string: √(gr) (string can only pull)

Explanation

A string can only pull (tension ≥ 0); minimum at top = √(gr). A rigid rod can push or pull; minimum speed at top = 0 (rod pushes outward when needed).

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