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What is the ball's horizontal displacement?

  1. Sep 28, 2005 #1


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    Ahh im already stuck on a question. I just need help getting started.

    Anyways this is the question

    A tennis player serves a ball horizontally, giving it a speed of 24 m/s from a height of 2.5 m. The player is 12 m from the net. The top of the net is 0.90 m above the court surface. The ball clears the net and lands on the other side. Air resistance is negligible.
    a)For how long is the ball airborne?
    b)What is the horizontal displacement?
    c)What is the velocity at impact?
    d)By what distance does the ball clear the net.

    I have no idea how to start this. I dont even know what i have. Can you please help me.
  2. jcsd
  3. Sep 28, 2005 #2


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    Science Advisor

    Do you know any formulas for motion in 2 dimensions?
  4. Sep 28, 2005 #3


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    ya i kno all of them
  5. Sep 28, 2005 #4
    Here are some basic kinematics equations you will need:

    Vf = Vi + at
    Xf = xi + ViT + 1/2aT^2
    xf - xi = 1/2(vi + vf)T
    Vf^2 = Vi^2 + 2a(xf - xi)

    Try to look at the problem again with those in mind and see where it takes you.
  6. Sep 28, 2005 #5


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    I can get the time like this but it doesnt help because i dont understand why it works.

    2.5=0 - 1/2(9.8)t^2

    By why does using 2.5 for height work because doesnt the ball hit the ground at the end.
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