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Homework Help: I'm lost. Help?

  1. Feb 15, 2009 #1
    1. The problem statement, all variables and given/known data
    A carton is given an initial speed of 3.0 m/s up a 22.0 degree plane. a.) How far up the plane will it go? b.) How much time elapses before it returns to its starting point? Ignore friction.

    2. Relevant equations
    F=ma


    3. The attempt at a solution
    I have no clue. If someone could point me in the right direction and try to explain what's going on I would very much appreciate it.
     
  2. jcsd
  3. Feb 15, 2009 #2
    I've been trying to figure it out. I know I'm supposed to break it into 2 equations, but I don't know how to express the 3.0 m/s velocity in the x equation.

    [tex]\sum[/tex]Fx=mg*sin[tex]\theta[/tex]=max

    [tex]\sum[/tex]Fy=FN-mg*cos[tex]\theta[/tex]=may=0

    Is that right? If it is I still don't know where to go from here
     
  4. Feb 15, 2009 #3

    jgens

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    Gold Member

    Use the equation vf^2 = vi^2 + 2(a_x)(s).
     
  5. Feb 15, 2009 #4
    But I don't know the time, nor the acceleration.
     
  6. Feb 15, 2009 #5

    jgens

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    Gold Member

    You have both the initial and final velocities so all you need right now is the acceleration in the x direction, which you can find by using mg = Fncos(theta) and a_x = gsin(theta).
     
  7. Feb 15, 2009 #6
    Oh, ok. Now I get it. You put an (s) in the equation which threw me off. I found the distance and the time it took to reach the max point, but how do I get the total time? Should I just double the time it took to get to the highest point?
     
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