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Homework Help: Linking Kinematics Equations

  1. Sep 20, 2011 #1


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    1. The problem statement, all variables and given/known data
    my friend is standing on the roof of my house trying to fix the satellite. Suppose he needs a wrench and asked me to toss one up to him. If i stand 20.0m away and toss the wrench to the top of the 10.0m tall building, what is the magnitude of the velocity with which I need to throw the wrench?

    2. Relevant equations
    Kinematic Equations.

    3. The attempt at a solution

    Vox = ? Vx = ? ax = 0 T = ? Distance in x direction = 20
    Voy = ? Vy = ? ax = -9.9 T = ? Distance in the y direction = -10

    I got a hint that said two kinematic equations need to be set equal to each other to solve for time and initial Vx velocity, but i have no idea how to set that up... Exam tomorrow... please help!!
  2. jcsd
  3. Sep 20, 2011 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    For these questions is always best to write down two lists: (a) A list containing all the things you do know; (b) A list containing all the things you want to know. So, in this case

    1. Vertical acceleration (-g)
    2. Horizontal Acceleration (0)
    3. Initial height (0)
    4. Initial horizontal displacement (0)
    5. Final height (10)
    6. Final x-displacement (20)

    Want to know
    1. Initial speed in x-direction
    2. Initial speed in y-direction

    So the trick now is to find two SUVAT equations, each which contain only one of the things you want to know and where you know everything else in the formula.
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