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Kinematic Equations 2 balls

  1. Oct 4, 2011 #1
    This problem has been giving me problems for the past two days and I cant figure it out :( please help. this is my first ever physics class.

    1. The problem statement, all variables and given/known data
    A rubber ball is shot straight up from the ground with speed v_0. Simultaneously, a second rubber ball at height h directly above the first ball is dropped from rest.

    Known:
    V_0 and Height of origional ball drop
    y_coll= h- ((gh^2)/(2v_0)^2)
    find:
    h_max

    2. Relevant equations

    Vx= Vxi+ax (tf-ti)
    Xf=Xi + Vxi + 1/2 ax (tf-ti)^2
    Vxf^2= Vxi^2+ 2ax (Xf-Xi)

    3. The attempt at a solution

    I got to the point where I found what I thought was h_max and got

    hmax= (V_0^2/g)- 1/2*V_0^2

    the website I am working on told me I am missing a term but I cant figure out what I am missing. :(
     
  2. jcsd
  3. Oct 4, 2011 #2

    gneill

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    The question is, what is the question? You didn't state what it is you're trying to find!
     
  4. Oct 4, 2011 #3
    how to find h_max
     
  5. Oct 4, 2011 #4

    gneill

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    Yes, but what is h_max supposed to represent?
     
  6. Oct 4, 2011 #5
    the maximum value of h for which a collision occurs before the first ball falls back to the ground?
     
    Last edited: Oct 4, 2011
  7. Oct 4, 2011 #6

    SammyS

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    I would have never guessed that.
     
  8. Oct 4, 2011 #7

    SammyS

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    If a ball is shot vertically upward, with initial velocity, v0, how long does it take the ball to return to its initial location?
     
  9. Oct 4, 2011 #8
    I know this book and website combination is not the most helpful thing in the world. Whaat I have done so far is pluged in Hmax for the Xf of the second kinematic equation and when I solved it I ended up getting v_0^2/g-1/2 v_o^2 which got me to where it said I was close but I was either missing a term or it was incorrect and I cant figure out whats wrong so I guess my question should be...what am I doing wrong
     
  10. Oct 4, 2011 #9
    sorry I didnt see that question...I am not sure the only thing I can think of is time final-time initial but that wouldnt help me. I really dont know


    from what I can think of it would equal the velocity over the gravity
     
  11. Oct 4, 2011 #10

    SammyS

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    If it wouldn't help, I wouldn't have asked it. It will definitely help to work that out.
     
  12. Oct 4, 2011 #11
    what I meant to say is my answer wasnt going to help me sorry for the unclarity
     
  13. Oct 4, 2011 #12
    I finnaly figured it out...thank you guys for the guidence
     
  14. Oct 4, 2011 #13

    SammyS

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    Good. The collision should occur just before the first rubber gets back to ground level.
     
  15. Oct 4, 2011 #14
    yeah thats what I got
     
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