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A heavy bob is attached to end A of a string of length 1.6 m whose other end O is fixed. It moves as a conical pendulum with the string making 60 deg with the vertical. Which of the following is correct? (g = 9.8 m/s²)

1. its period of revolution is 4pi/7 sec
2. the tension in the string is double the weight of the particle
3. the velocity of the particle = 2.8*sqrt(3) m/s
4. the centripetal acceleration of the particle is 9.8*sqrt(3) m/s²

Correct answer: the tension in the string is double the weight of the particle

Solution

Vertical balance gives T = mg/cos(60 deg) = mg/(1/2) = 2mg, so the tension is twice the weight.

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