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Homework Help: Is work being done?

  1. Dec 5, 2004 #1
    A rock mass 2.2 kg is attached to a string of length 1 m is twirled around in a perfect circle as a speed of 2.5m/s. Calcualte the work done on the mass by the tension force exerted on the rock by the string during one revolution of the rock. Ignore the effect of gravitational forces.

    Since displacement is 0, would work be done = 0J?
  2. jcsd
  3. Dec 5, 2004 #2
    sounds good to me
  4. Dec 5, 2004 #3
    The tension is perpendicular to the direction of motion - so it should be 0.
  5. Dec 5, 2004 #4
    can anyotne please explain to me why is displacement = 0???? if displacement was 0, then there would be no circular motion of the rock right?

  6. Dec 5, 2004 #5

    Doc Al

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    Staff: Mentor

    Don't confuse displacement with distance. Displacement measures your position relative to some point. If you go around in a circle, ending up where you started, your displacement from your starting point is zero. (But the distance you traveled is the circumference of the circle.)

    FYI: The reason why work is zero in this case is that given by futb0l: the force is perpendicular to the velocity.
  7. Dec 5, 2004 #6
    Just think of work as the change in energy. The Rock has the same energy in it anywhere in its circular path, so no work :smile:
  8. Dec 6, 2004 #7
    hmmm awrite got it now... thanks much :)
  9. Dec 7, 2004 #8
    But different force directions...........
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