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Finding Time with 3 unknowns

  1. Sep 20, 2009 #1
    3rd week in AP physics... can't figure this out :'(

    1. The problem statement, all variables and given/known data
    delta X = 20m
    delta Y = -1.5m
    angle = 10 degrees

    basically, a car goes off a 10 degree ramp and lands 20 meters away and the delta Y is 1.5m... my assumption is that I need to find T first.


    2. Relevant equations
    we are given 4 equations:
    delta X = VxoT
    Vy = Vyo + AyT
    delta Y = VyoT + (1/2)AyT^2
    Vy^2 = Vyo^2 + 2Ay(delta Ymax)



    3. The attempt at a solution
    i have no attempt.
     
  2. jcsd
  3. Sep 20, 2009 #2

    rock.freak667

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    y=y0+vxt-1/2gt2

    you want to find t when y=0 (y0=1.5)
     
  4. Sep 20, 2009 #3

    I don't know what Vx is.
     
  5. Sep 20, 2009 #4

    rock.freak667

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    the angle θ=10

    so vx=vcosθ

    and vy=vsinθ


    Also I made a typo,the equation should be


    [tex]y=y_0 +v_y t -\frac{1}{2}gt^2[/tex]


    (not vx in it)
     
  6. Sep 20, 2009 #5
    A hint: You must plug one equation into another on this one, this will result in the removal of Vo from an equation and leaving only time.
     
  7. Sep 20, 2009 #6
    I still need help, I know i need to plug in equations into each other but i'm not sure which ones
     
  8. Sep 20, 2009 #7
    figured it out, the key was

    t = (20.33/v)

    then i plugged that into this eqn:

    delta X = VxoT
     
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