Critical Speed & Looping
A point mass ' ' attached at one end of a massless, inextensible string of length ' ' performs a vertical circular motion and the string rotates in vertical plane, as shown in the diagram. The increase in the centripetal acceleration of the point mass when it moves from point A to point C is [ acceleration due to gravity.]

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Answer: (b)
- From the figure, A is the top and C is at the level of O, so C is below A.
- Energy:
- Increase in
- So the answer is (b) 2 g.