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Calculate acceleration due to gravity

  1. Jan 1, 2015 #1
    1. The problem statement, all variables and given/known data
    A stone is thrown horizontally from a cliff on a different planet with a speed of 10 m/s. The cliff has height 200m, and takes 4 s to hit the ground. Assume no air friction. What is the acceleration due to gravity on this planet.

    2. Relevant equations
    Δy = v0t + 1/2 at2

    3. The attempt at a solution
    I thought the initial vertical velocity would be 0 since it's thrown horizontally, so the first term of the equation disappears. And they give you t = 4, so I did 200*2/16 = 25 m/s^2.
    But apparently the answer is 5 m/s^2.
    Why?
     
  2. jcsd
  3. Jan 1, 2015 #2

    Bystander

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    One half "a" times "t" squared.
     
  4. Jan 1, 2015 #3

    SammyS

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    Your answer (as well as your analysis) looks good to me !!

    I agree it's 25 m/s2 .
     
  5. Jan 1, 2015 #4

    Bystander

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    Get used to facing problems/exercises in which people have swapped quantities/values to be found from the problem statement for other "given" values, and failed to correct answer keys.
     
  6. Jan 1, 2015 #5
    Okay, so I'm right. Thank you.
     
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