# What speed will an object fall?

1. Jun 21, 2008

### ATCLanser

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. Jun 21, 2008

### FredGarvin

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]

http://www.juliantrubin.com/bigten/galileofallingbodies.html

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

### Hootenanny

Staff Emeritus
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.

4. Jun 21, 2008

### FredGarvin

True. However it should be pointed out that drag is not proportional in any way to mass either. It is a function of geometry.

5. Jun 22, 2008

### aniketp

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.

6. Jun 22, 2008

### stewartcs

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.

CS