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Gravity in other planets

  1. Nov 26, 2009 #1
    1. The problem statement, all variables and given/known data
    On Planet Plutnik the acceleration due to gravtiy is not 9.8m/s^2.
    An object dropped is found to fall the final 15m of its trip in 2seconds.
    It lands with a speed of 10m/s. Find the acceleration due to gravity on Planet Plutnik.



    2. Relevant equations
    d = vit + 1/2at^2
    vf^2 = vi^2 + 2ad



    3. The attempt at a solution

    d = vit + 1/2 at^2

    vi would be 0 in this case right?
    and distance is 15m with final velocity 10m/s
    vf^2 = vi^2 + 2ad
    10^2 = 0 + 2a15
    100 = 30a
    a is 1/3 m/s^2 ?
     
  2. jcsd
  3. Nov 26, 2009 #2

    mgb_phys

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    Not necessarily
    It doesn't say it was dropped 15m, it says the final 15m of it's fall was 2s

    You need to find what height it was dropped from.
     
  4. Nov 26, 2009 #3
    I was just looking at this, we know that in the 15m of the fall (from 15m to 0m in 2 seconds) and the final velocity is 10 m/s. Since it is a free fall question, the acceleration is constant, so using the formula:

    y = y0 + 1/2(V0 + V)t = 0 = 15 + 1/2(v0 + 10)2

    solve for v0 then plug it into:

    Vy^2 = Vy0^2 + 2a(x-x0) solve for a and you are done
     
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