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Homework Help: Ball Velocity Question

  1. Sep 23, 2007 #1
    1. The problem statement, all variables and given/known data
    A ball is thrown directly downward, with an initial speed of 7.75 m/s, from a height of 30.8 m. After what time interval does the ball strike the ground?

    3. The attempt at a solution
    The way I understand it is that since it is freefalling, it is moving at 9.8m/s towards that ground, thereby I neglected the 7.75m and did 30.8/9.8 = 3.14s..however it is wrong and the similar problem book is even numbered therefore cannot work through it backwards.. Any help?
  2. jcsd
  3. Sep 24, 2007 #2


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    I'm afraid that is incorrect; the ball is accelerating at 9.81m/s2 which makes a big difference. I'm assuming that your doing a mechanics course, so which kinematic equations do you know?
  4. Sep 24, 2007 #3
    Actually just in a standard Calc based physics, thereby I have no equations
  5. Sep 24, 2007 #4


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    Hint: The ball is moving at a constant acceleration.

    You should have plenty of constant acceleration equations in a Calculus based Physics course to relate velocity, displacement, acceleration, and time.

    If not, check out these...


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