A stone hangs by a fine thread from the ceiling. Help please.?

A stone hangs by a fine thread from the ceiling, and a section of the same thread dangles from the bottom of the stone (Fig.4–36). If a person gives a sharp pull on the dangling thread, where is the thread likely to break: below the stone or above it? What if the person gives a slow and steady pull? Explain your answers.

I have a few questions, does the dangling part of the thread have T ? If it does is it equal to the tension in the upper part of the string (above the stone) or is it substantially smaller ?

Here's what I think will happen:

When you pull slowly, the system is in equilibrium. As you increase the force 'f', mg being constant, at a certain point the tension becomes greater than the maximum tension the string can tolerate and hence, the upper string breaks.

Is that true ? Or is it that when you pull slowly, the tension has time to distribute above and below the stone, but since the upper part of the string has to 'carry' the weight of the ball, the tension in the upper part is greater and the string snaps ?

 I don't know how to think of it when the string is being pulled quickly/fast. If the latter was true, then I'd say that the tension has no time to be distributed but I wouldn't know why the lower string breaks

1 Answer

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  • 1 month ago

    The stone has significant inertia. A quick pull will exceed the breaking strength of the lower string before the mass is able accelerate significantly. the lower string will break.

    With a slow pull, the tension in the lower string is only the force of the pull being applied while the tension in the upper string is the sum of the pull being applied on the lower string and the pull being applied by the stone. Upper string breaks.

    • derfram
      Lv 7
      1 month agoReport

      I live in the real world where the string will have at least a bit of stretch. If the upper string does not stretch, because the mass does not move, then the tension in the top thread can not increase. Answer may be different if the string was totally non-elastic.

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