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Homework Help: Acceleration of rock due to gravity

  1. Nov 4, 2008 #1
    A rock is dropped from rest at the top of a cliff 125 cm high.

    a) At what speed does it strike the ground?

    b) How long does it take?

    To find the velocity the equation used is v = u + at

    I know that (u = 0) as it's from rest and g = 9.81 ms (gravity)

    But I just need help on how to get the velocity when the time is not stated!

    I have the answers but I'm not sure how to reach them

    a) 49.5 ms

    b) 5.05 ms
  2. jcsd
  3. Nov 4, 2008 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    You have two options:

    (1) Use conservation of energy

    (2) Use another kinematic equation which involves velocity, distance and acceleration
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