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Finding the height of a building that a projectile is thrown from using kinematics

  1. Jun 15, 2011 #1
    1. The problem statement, all variables and given/known data
    A 0.21 kg rock is projected from the edge of
    the top of a building with an initial velocity of
    7.82 m/s at an angle 56 above the horizontal.
    Due to gravity, the rock strikes the ground at
    a horizontal distance of 10.5 m from the base
    of the building.

    How tall is the building? Assume the
    ground is level and that the side of the build-
    ing is vertical. The acceleration of gravity is
    9.8 m/s2 .
    Answer in units of m.


    2. Relevant equations

    Kinematics equations. Pythagorean Theorem: A +B = C

    3. The attempt at a solution

    i tried to think about what I needed, and what equation would help me find it. In this case, the height h, I chose the following equation:

    H = Vy - VoY / 2A from the initial kinematics equation of Vy = Voy + 2AH

    From here, however, I am unsure how to determine Vy, which is the only variable I would need.
     
  2. jcsd
  3. Jun 15, 2011 #2
    Re: Finding the height of a building that a projectile is thrown from using kinematic

    All those variables in the exponent section should have exponents of 2 themselves.
     
  4. Jun 15, 2011 #3
    Re: Finding the height of a building that a projectile is thrown from using kinematic

    Vy = [itex]vsin \Theta[/itex]
     
  5. Jun 15, 2011 #4

    Vim

    User Avatar

    Re: Finding the height of a building that a projectile is thrown from using kinematic

    You'll have to split your initial velocity into x and y components. (Use the Pythagorean theorum, your initial velocity will be the hypotenuse.)

    Once you've established what the initial y-velocity is, use your kinematics equations to find the final y-velocity. ( vf = vi + a*t )
     
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