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Homework Help: Help- throwing apples

  1. Sep 20, 2005 #1
    Help me please I've been stuck on this problem for an hour now.....

    John throws and apple from a height of 1.3 m with velocity of 2.4 m/s. Will it reach his friend in a treehouse 5 m above the ground?

    My book gives the answer "No, it will only reach 1.6 m," but I really wanna know how to do this. Any help is greatly appreciated. Thanks!
     
  2. jcsd
  3. Sep 20, 2005 #2
    I would think you'd need to know the angle of the throw and how far away the friend is, but I'm quite a beginner so I'm not sure.
     
  4. Sep 20, 2005 #3

    Doc Al

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    Staff: Mentor

    Consider conservation of energy. Will the apple have enough energy to make it to that height (regardless of the angle it's thrown)?
     
  5. Sep 20, 2005 #4
    Whoops, sorry about the homework help violation....in such a rush to figure this out that I didnt see the rule.

    I'm pretty sure he wants us to use a Free Fall kinda thing, with an equation like Vf=Vi+2(a)(t), but not all those factors are there. This is basic physics stuff, we're studying like -9.81 acceleration for gravity, and how to find displacement and velocity and all that.
     
  6. Sep 20, 2005 #5

    Doc Al

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    If you threw the apple straight up at that speed, how high would it go?
     
  7. Sep 20, 2005 #6
    Well that's what the question is asking, and I assume that's displacement. Displacement in our book is

    D= .5(Vi+Vf)t

    I have Vi(2.4), and Wf would be 0 once it reached the top, but I don't know t. Am I using the wrong formula here? I have no idea what to do.... :frown:
     
  8. Sep 20, 2005 #7

    Doc Al

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    Staff: Mentor

    You can find the time using the definition of acceleration:
    [tex]v_f = v_i + at[/tex]
     
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