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Very simple gravity question on another planet.

  1. Sep 21, 2005 #1
    Alright I am obviously retarded since I am unable to figure this question out.

    The question is:

    You have just landed on Planet X. You take out a ball of mass m, release it from rest from a height of h and measure that it takes a time of t to reach the ground. You can ignore any force on the ball from the atmosphere of the planet.

    My guess as to what the answer would be is: m*((h/t)/t)

    since weight equals mass times acceleration and the acceleration equals change in velocity over time. I figured it starts at 0 and ends at h, so the change in velocity is h/t. Where am i going wrong with this?

    The error or hint I am recieving is "Your answer is off by a multiplicative factor."

    Anyone have any ideas? I have to answer this problem within the next 2 hours and I still cant figure it out. I would try changing my original answer above a bit, but if I guess anymore I get zero credit for the problem.
    Last edited: Sep 21, 2005
  2. jcsd
  3. Sep 21, 2005 #2

    Doc Al

    User Avatar

    Staff: Mentor

    h/t is the average velocity during the fall, not the change in velocity. Since it starts with speed = 0, what must be the final speed after falling the distance h?
  4. Sep 21, 2005 #3
    got it... (2*h*m)/t^2
    Last edited: Sep 21, 2005
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