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Work of a moving bowling ball

  1. Oct 20, 2013 #1
    1. The problem statement, all variables and given/known data

    A bowling ball of 7.21kg is thrown, it has an initial velocity of 12.5m, if his mouvement happens over 1.24m, what is the work of the bowling ball.


    2. Relevant equations

    W = FΔd
    W = F (Cos∅)Δd

    3. The attempt at a solution

    I think this is a trick question, but I'm not sure... to calculate the force of the bowling ball I would need to find it's mass and acceleration. But considering we don't have Δt or V2 we can't find the acceleration. Anyone know if I'm right?
     
  2. jcsd
  3. Oct 20, 2013 #2
    I think that you wrote a sort of summary rather than the actual text of the problem. Is this so?
    As you wrote it does not make much sense to me.
     
  4. Oct 20, 2013 #3

    rcgldr

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    I assume that it's the final speed of the bowling ball that is 12.5 m/s, and that the initial velocity is zero. From the way the problem is worded, the distance of the movement doesn't matter, since the work done on the bowling ball equals the increase in kinetic energy. Assuming the initial KE is zero, what is the final KE?
     
  5. Oct 20, 2013 #4
    No, as i understood the question the ball's initial velocity is 12.5m/s, but it does not say if it accelerates, or stays at a constant speed. Is the work done equal to the increase of Ek? That's the first i've heard of this...
     
  6. Oct 20, 2013 #5

    rcgldr

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    That doesn't make sense. What was the source of the ball's initial velocity? If that is the initial velocity, you need more information to determine the final velocity.

    Yes, it's a basic law of physics. Work = ΔEk (change in kinetic energy).
     
  7. Oct 20, 2013 #6
    Well it doesn't specify, it only says it's thrown, so i'm guessing someone threw it :P. That's all the information given; it is possible that this is a trick question... I just want to be sure.
     
  8. Oct 20, 2013 #7

    rcgldr

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    Since only one velocity value is given in the problem I would assume it's the final velocity. I'm not sure what the 1.24 m movement information is to be used for. If this was the vertical distance the ball traveled, then the potential energy would decrease by m g h, and Ek would increase by m g h, but this doesn't appear to be the intent of the problem.
     
  9. Oct 21, 2013 #8

    PhanthomJay

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    I believe the problem is stating that the ball leaves the thrower's hand with an initial velocity of 12.5 m/s, and it is asking for the work done on it during its 1.24 m movement while it is still in the thrower's hand, statrting from rest as rcgldr notes, and having a final velocity of 12.5 m/s at release. The 'final' velocity in the throwers hand is the 'initial' velocity when the ball leaves the hands. Problem could have been worded better, I suppose.
     
  10. Oct 21, 2013 #9
    I doubt that this is the actual text of the problem, in a book. Just look at the sentence structure.
    It may help if the OP takes an extra minute to copy the original text.
     
  11. Oct 21, 2013 #10
    I swear to you this is the original question, not moified. It was not from my texted book, it written exacly like that on a test I recently did. I agree with you guys the wording he chose is terrible. The confusing part was that the '' initial velocity'' of the ball is when it is thrown, it is therefore the final velocity of his throwing movement, and obviously the initial velocity is 0.

    However you guys were right, you can use conservation of energy Ec1 = Ec2 Or ΔEc to find the answer. you can also use the kinetic equation that does not include Δt and solve for the acceleration. From there use F = ma or simply substitute them all into the W = FΔd.

    Thanks for the help guys!
     
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