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How to find minimum speed?

  1. Feb 14, 2013 #1
    in a baseball game the batter hits the ball and launches it upward at n angle of 52.0 degrees...\


    I used V_x=Vocos(/theta)+a_xt to solve for V_x and got 31.6m/s which is wrong. what should I do.
     

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  3. Feb 14, 2013 #2

    tms

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    You are mixing the ball and the fielder together. First solve for the ball, finding out where and when it lands, then figure out how the fielder can get there.
     
  4. Feb 14, 2013 #3
    I used the same equation and had 2.3 s and had 19.56 m/s. is that process correct?
     
  5. Feb 14, 2013 #4

    haruspex

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    I make it 2.47s. Pls show your working.
    I can't do part b because I don't know the layout of a baseball pitch. In fact, I don't understand how you're supposed to know which direction the ball went.
    I note also that the question makes no allowance for the height off the ground when the ball was struck.
     
  6. Feb 14, 2013 #5
    so I do 38 meters/ 2.47 seconds= 15.38 m/s .?
     
  7. Feb 15, 2013 #6

    tms

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    It's called a field or a diamond. A pitch in baseball is the throw the pitcher makes at the batter.
    I think we are to assume that ball goes straight at the center fielder.
    I think we are to assume it is to be caught at the same height it was hit from.
     
  8. Feb 15, 2013 #7
    I still dont understand what to do
     
  9. Feb 15, 2013 #8

    haruspex

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    First, a correction. I don't get 2.47s for the flight time of the ball, I get 6.10s. Sneakatone, if you do not get that pls post your working. If/when you have the flight time right, find where the ball will land (as tms already instructed).
     
  10. Feb 15, 2013 #9
    I did 0=38cos(52)+(9.8)t


    45/6.1= 7.4 m/s
    would that be correct?
     
  11. Feb 15, 2013 #10

    tms

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    Why did you do that? You seem to be mixing up the horizontal and vertical components, among other things. Try using symbols to set up your equations; it will be clearer what is going on and where you are going wrong. It is best to proceed systematically. Start by drawing a diagram showing the forces on the ball. Then write down the kinematic equation for the vertical direction, then solve it for the time taken to go up and down.
     
  12. Feb 15, 2013 #11
    this is how i see it
     

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  13. Feb 15, 2013 #12

    tms

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    The ball does not keep going up without regard to gravity. What is the shape of the ball's trajectory?

    And the distance the fielder is from the batter has no influence on the ball's trajectory.
     
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