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Suppose the bob of a stationary pendulum is given a sharp hit to impart it some horizontal speed. Now what are the conditions for the string to become slack after rotating a particular angle?

  • resultant centripetal force should be zero.

    -tension in the string should be zero

    Or what?

    And when the string becomes slack, does it have GPE only or GPE and KE both?

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closed as off-topic by ACuriousMind, CuriousOne, Gert, user36790, Asher May 3 '16 at 4:50

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  • $\begingroup$ I don't think that you can properly analyze this problem without taking tensile strain into account which means the possible presence of elastic potential energy in the system as well. $\endgroup$ – dmckee May 2 '16 at 18:10
  • $\begingroup$ The instant it becomes slack, the tension in the string will equal zero. $\endgroup$ – lemon May 2 '16 at 18:41
  • $\begingroup$ Suppose the string is inextensible. When it becomes slack,i.e, when the tension equals zero, should the centripetal force also equals zero? $\endgroup$ – ADITI SAINI May 3 '16 at 1:45