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Homework Help: Downward Acceleration

  1. Sep 18, 2008 #1
    1. The problem statement, all variables and given/known data
    You plan on throwing an egg at someone from the roof. You throw the egg downward at 2.0 m/s from a height of 10.0 m above the person's head. The person walks toward the building at 1.25 m/s. How far from the building should the person be when you throw it?

    2. Relevant equations

    V= delta x/ delta t

    3. The attempt at a solution

    delta t = 5 seconds

    delta x =(1.25 m/s)(5 seconds)

    They should be 6.25 m from the building.

    Could someone please doublecheck this for me?
  2. jcsd
  3. Sep 18, 2008 #2
    If the 2.0 m/s is an initial velocity, the egg would be accelerating downward and the time it takes to traverse the 10m distance would be much less than 5 seconds.
  4. Sep 18, 2008 #3
    Thanks for the reply. I tried re-evaluating this using v final squared = v initial squared +2at
    and v final = v initial + at

    and came up with a time of 1.23 s.

    Is this correct? I'm not sure if I should use -9.8 or 9.8 for the acceleration of gravity.
  5. Sep 18, 2008 #4
    Since the egg is traveling in the same direction the gravitational force is acting, the acceleration will be a positive value for this case. Just be careful for future problems as direction is a key factor for the sign of the acceleration value. A way to think of it is the egg is being thrown downward therefore the acceleration will increase the velocity, so the equation should match this property. I believe you have come up with the correct time.
  6. Sep 18, 2008 #5
    Gotcha. Thanks so much for your help.
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