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With what minimal horizontal velocity can you throw a stone

  1. Jun 29, 2017 #1
    1. The problem statement, all variables and given/known data
    With what minimal horizontal velocity can you throw a stone from position A so it it manages to fly over position B.

    the distance between A and B is 40m
    the height of position A is 20m
    the height of position B is 10m

    2. Relevant equations


    3. The attempt at a solution
    I have tried to solve it by making the distance 41m getting the time then solved basic velocity equation and got 28.67m/s, but that probably isnt correct
     
  2. jcsd
  3. Jun 29, 2017 #2

    BvU

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    Science Advisor
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    Gold Member

    Hello goku, :welcome:

    What is your question ?
     
  4. Jun 29, 2017 #3
    Pls give is the exact question as or would be easier.. Consider reading guidelines for other information
     
  5. Jun 29, 2017 #4

    gneill

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    Staff: Mentor

    Yes, probably not correct. Can you please show the details of the calculations that you attempted?
     
  6. Jun 30, 2017 #5
    not much but here 76kQ_G.jpg
     
  7. Jun 30, 2017 #6

    Merlin3189

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    Gold Member

    Your working looks fine to me.
    The issue is in taking the horizontal distance as 41m. This is arbitrary. Since you don't know the size or shape of the stone you can't know how much clearance to give. You just have to work with the given 40m and say that it has to go further than that. Maybe only by 1mm or maybe even less. So using 40m gives you a speed which you must exceed. That's all you can say.

    It's a bit of a mathematical game: you make a "model" - an idealised situation where you ignore some inconvenient or unknown details. Positions and objects become "points" with no size. Here the stone would hit B at 28m/s, but miss at any greater speed.
     
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