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Homework Help: Calculating acceleration due to gravity on a planet

  1. Sep 11, 2009 #1
    1. The problem statement, all variables and given/known data

    The data is taken from a graph. The initial velocity is 31m/s. I found the horizontal velocity to be 21m/s. The time the ball travels is 5 seconds. The total distance the ball travelled is 105m. The ball lands at the same vertical level at which it starts. Air resistance can be neglected.

    2. Relevant equations

    Im pretty sure I have to use this equation, where t= 2.5.

    v = v(initial) + at

    I used the pythagoreum theorem to find the initial vertical velocity to be 22.8m/s. Then divided it by 2.5. What I came up with, -9.12, which is wrong.

    I just cant find the acceleration due to gravity. It looks straight forward but I am missing a step. Any ideas?

  2. jcsd
  3. Sep 11, 2009 #2


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    Your method appears to be correct and the answer follows from the numbers that you gave. If the answer is incorrect, then you need to make sure that you read the graph correctly. When you say "the initial velocity is 31 m/s", you mean the initial speed is 31 m/s, right?
  4. Sep 11, 2009 #3
    Here is a link to the graph, which plots the velocity over time (sorry i didnt think to add it)

    https://wug-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?cc/DuPage/phys2111/fall/homework/Ch-03-04/golfball_plot/golfball_plot-1.jpg [Broken]

    Thanks for the help!
    Last edited by a moderator: May 4, 2017
  5. Sep 11, 2009 #4
    Ahh, it was +9.12. However, I am not sure as to why it is positive.
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