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My profesor gave us this (I think) impossible problem to do.

  1. Apr 18, 2005 #1
    She may want us to assume something but I'm not sure and can't ask her for a while. There just isn't enough info I think. here it is.

    A ball is rolled on level floor a distance of 3.5m to another person. The ball made 15 revolutions.

    a) asked for diameter of the ball which is easy and I got that only.

    if the rolling time is 10 seconds...

    b)what is angular acceleration?
    c)what is linear acceleration?
    d)what is final velocity when it is stopped?

    I see no way to answer b-d without more info. Does anyone have any idea what she wanted us to assume? This is all the info she gave. I guess D could be 0 but I'm not sure if thats what she's looking for.

  2. jcsd
  3. Apr 18, 2005 #2
    Was the ball stopped at 0s?
    Because if it was stopped at the start and stopped at the end it should tell you something about the acceleration.
  4. Apr 18, 2005 #3
    it is pushed by someone and stopped by the person on the other end of that 3.5m. So since it was rolled by someone, I would assume initial velocity is 0 untill it is rolled.
  5. Apr 18, 2005 #4


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    If the answer isn't 0, this is a very poorly worded question. If it is, it's just a poor question. As for the rest, the average acceleration (assuming that's what you want) is defined the same way as the average velocity, which is total distance covered (or total change in position) divided by total time.
  6. Apr 18, 2005 #5

    I don't know about that... ANGULAR ACCELERATION is described as w(omega) w2-w1/t2-t1

    Is w supposed to be the distance?

    And I still have no idea on the linear acceleration.
    maybe V-Vinitial/t ?
  7. Apr 18, 2005 #6


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    w is angular velocity. Does this help?
  8. Apr 18, 2005 #7
    Well, so how could I answer b,c,d? I'm looking for an answer if you don't mind, not just some help.

    I want to discuss this with the professor when I get the chance. I even asked the tutor at school and he's says he's in a huge disagreement with her over this problem.
  9. Apr 18, 2005 #8

    Doc Al

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    Are you sure about it being a level floor? If the floor were slanted, this problem would make more sense. In that case you'd have linear and angular acceleration and a final velocity to calculate.
  10. Apr 18, 2005 #9
    Yes its level. I guess if you could explain it otherwise, she'd accept it.

    How would you explain all 3 of those answers are 0?
  11. Apr 18, 2005 #10


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    The answers are supposed to be 0? In that case, I think they want you to assume the ball is at rest at the beginning and end, which means neither its angular velocity or linear velocity change, and the average acceleration is 0 for both. The last question makes me angry, and I would refuse to answer it.
  12. Apr 18, 2005 #11

    Doc Al

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    As StatusX said, the way this problem is worded the answers are zero.

    Assuming the ball rolls without slipping, its speed after leaving the first person's touch is constant until it reaches the other person. Acceleration (while it's rolling) = 0.
  13. Apr 18, 2005 #12
    But wouldn't acceleration be decceleration because it would slow down as it goes?

    But thats weird because as its pushed, the acceleration would have to rise, but it will slow down eventually so its decelerating.

    This problem sucks.
  14. Apr 18, 2005 #13


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    Go with your initial instincts. For whatever reason, you do not have all the information about the problem. Nobody here has decuced the missing information yet, and it is very unlikely they will.
  15. Apr 18, 2005 #14
    assuming ideal conditions then you can neglect friction and what not. which is most likely the nature of this problem.

    as i see it, like previously stated, all the answers are zero.
    Last edited: Apr 18, 2005
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