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Falling rock

  1. Jan 9, 2007 #1
    1. The problem statement, all variables and given/known data
    - A guy sees a rock falling from a plateau. He estimates the last third (1/3) of the rocks fall to last for 1,3 sec. Air resistance doesn't need to be taken into consideration.

    - How far/what distance has the rock fallen?

    2. Relevant equations
    None given

    3. The attempt at a solution
    I was thinking of making a logarithmic equation out of it:

    f(x) = b*x^a, f(x) = distance travelled, b = ??, x = 1,3 sec or (1/3) ? and a = 9,82 m/s^2

    I am by no means sure about this attempt. Thanks on beforehand.
  2. jcsd
  3. Jan 9, 2007 #2


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    Staff: Mentor

    The relevant equations are the kinematic motion equations. They relate the position and velocity and acceleration of an object versus time. What is the velocity of a mass versus time, based on the acceleration of gravity? What is the position of an object versus time, based on its initial velocity and its acceleration? How do these equations help you solve this problem?
  4. Jan 9, 2007 #3


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    Science Advisor
    Homework Helper

    The last third by distance or by time?

    If by time, the problems very easy. If by distance, it will take a little thought. From the initial position at the time the person first saw the rock and with an initial velocity, it took 1.3 seconds to complete the fall. You need to figure out how to come up with a one variable expression for the initial position and a one variable expression for the initial velocity (both the same variable).
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