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Homework Help: How to incorporate the initial vellocity

  1. Oct 26, 2003 #1
    I'm having difficulty with the following problem: What is the average force exerted by a shot-putter on a 7.0 kg shot if the shot is moved through a distance of 2.8 m and is released with a speed of 13 m/s.

    I know that I have to use the formula F=ma. The mass is obviously 7.0 kg, but I don't know how to find the horizontal component of the acceleration of the shot. I don't know how to incorporate the initial vellocity and the distance the shot travels. I would appreciate any help. Thanks.
     
  2. jcsd
  3. Oct 26, 2003 #2

    jcsd

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    Use the formula:

    v2 = u2 + 2as
     
    Last edited: Oct 26, 2003
  4. Oct 26, 2003 #3
    what do the variables stand for?
     
  5. Oct 26, 2003 #4

    jcsd

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    v is final velocity (13ms-1), u is initial velocity (assume this to be zero), a is accleration, s is displacement (distance).
     
  6. Oct 26, 2003 #5
    ok, so that gives an acceleration of 2.32m/s^2. But it doesn't make sense that this would be the acceleration to plug into the formula F=ma. I know that the correct answer to the problem is 210 N.
     
  7. Oct 26, 2003 #6

    jcsd

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    Show me your workings, using the above equations I got an answer of 211.25 N (210 N if I'd rounded the accleration to 3 ms-2).
     
    Last edited: Oct 26, 2003
  8. Oct 26, 2003 #7
    I got it! I've been making such a dumb mistake. When I used v^2=u^2 + 2as, I kept forgetting to square the 13! Now i'm getting the right answer. Thanks a lot for helping me out here.
     
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