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Homework Help: Projectile motion (ground to ground)

  1. Jun 21, 2015 #1
    1. The problem statement, all variables and given/known data
    In the figure, a baseball is hit at a height h = 1.30 m and then caught at the same height. It travels alongside a wall, moving up past the top of the wall 1.1 s after it is hit and then down past the top of the wall 3.9 s later, at distance D = 42 m farther along the wall. (a) What horizontal distance is traveled by the ball from hit to catch? What are the (b) magnitude and (c) angle (relative to the horizontal) of the ball's velocity just after being hit? (d) How high is the wall?

    2. Relevant equations
    I have the kinematic equations and equations for motion (while in flight)

    3. The attempt at a solution
    known solns:
    ay = -g = -9.8m/s2
    v0y = 29.89 m/s
    vfy = -29.89 m/s
    Δy = 0
    t= 6.1s

    im stuck at this point. i think maybe i can set the v at max height equal to the x component of v0?
  2. jcsd
  3. Jun 21, 2015 #2


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    Consider its horizontal velocity for the time it is above the wall.
  4. Jun 21, 2015 #3
    velocity for the time the ball is over the wall,
    v = Δd/Δt
    = 42m / 3.9
    = 10.77m/s.
    But this is average velocity, if ax is constant and vx is constant then the avg velocity is equal to v at any point?

    vavg = v0x = v0cosθi,
    is the x component of v0.

    How do you type unit vecotors i,j, and k with hats?
  5. Jun 21, 2015 #4


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    For the hat, use Latex. Putting a consecutive pairs of hash symbols(#) starts and ends a Latex string. Using dollar symbols instead puts the Latex on a line of its own. A hat over a character is achieved by writing \hat in front of it. Put a space after hat. If it is to go over something more complicated than a single character, use curly brackets: \hat{x^2} will produce ##\hat{x^2}##.
    You can see how others have written latex by right-clicking on the generated text in their post and selecting View math as. You can then cut and paste to produce your own.
    Sometimes the Latex refuses to work properly even though what you've written looks right. It's usually because you've included an unusual ASCII character or have some font change within it. Latex is jealous - in the Latex string, all must be Latex.
    Always use the Preview button to check the Latex before posting.
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