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Homework Help: Kinematics/free fall objects help.

  1. Oct 9, 2011 #1
    In my honors course we are covering kinematics concepts. There was this problem which stumbled me but then I figured out what I did wrong. I just want to make sure my concept was right. Here is the problem...

    A diver springs upward with an intial speed of 1.8 m/s from a board that is 3 meters above
    the surface of the pool (his displacement is y = -3m). What is the highest point he reaches above the water.

    So this was my equation

    vi = 1.8 m/s
    vf = 0 m/s
    a = -9.8 m/s2
    x = ?

    Solved the equation and got x = 3.16 or 3.2

    So the part that kind of confused me in the begining was that I only had vi and vf. There had to be one more piece to solve the equation. Thats when I realized that gravity works even when the object has a positive velocity in the upward y direction. But then I started
    doubting my self so Im kind of confused.
  2. jcsd
  3. Oct 9, 2011 #2
    So are you confused about when to use -9.8 as the acceleration?
  4. Oct 9, 2011 #3
    Yeah basically. I was confused because he was going up and I kept thinking gravity in terms of falling down. So I wanted to make sure that gravity is the same when going up as well.
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