Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Science Advisor

    Last edited: Jun 21, 2008
  4. Jun 21, 2008 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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


    User Avatar
    Science Advisor

    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


    User Avatar
    Science Advisor

    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.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: What speed will an object fall?
  1. A falling object (Replies: 12)