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What speed will an object fall?

  1. Jun 21, 2008 #1
    I am looking for a formula to determine what speed an object will fall with a known height and weight. For example a 220 pound man falls from 65 ft, what speed will he be going when he hits the ground?
  2. jcsd
  3. Jun 21, 2008 #2


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    You do know that the speed an object falls is independent of its weight...right? The equations for constant acceleration are very well known in intro physics courses.

    http://selland.boisestate.edu/jbrennan/physics/notes/Motion/constant_acceleration_formulas.htm [Broken]

    Last edited by a moderator: May 3, 2017
  4. Jun 21, 2008 #3


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    I know that you know this Fred, but for the benefit of the OP I will mention the caveat that an objects' instantaneous velocity is only independent of mass provided that the effects of drag are ignored.
  5. Jun 21, 2008 #4


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    True. However it should be pointed out that drag is not proportional in any way to mass either. It is a function of geometry.
  6. Jun 22, 2008 #5
    There is a simple derivation for the formula below.
    The kinetic energy at the moment the object hits the ground is 0.5mv^2 which is equal to its potential energy at given height "h"
    Thus 0.5mv^2=mgh
    And v=(2gh)^0.5 which is independant of the weight.
  7. Jun 22, 2008 #6


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    This is only true if the drag force is ignored (as pointed out previously by Hootenanny and Fred). In real life it is not normally ignored.

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