Lever Word Problem

Date: 01/14/2003 at 21:30:06
From: Purdy Skwakins
Subject: Lever word problems

If a person has a 3-foot wrecking bar and places a fulcrum 3 inches 
from one end, how much can he lift if he applies a force of 50 pounds 
to the long end?

Date: 01/16/2003 at 10:38:38
From: Doctor Ian
Subject: Re: Lever word problems

Hi Purdy,

The key idea is that the amount of work is the same on both ends of
the lever. And work is equal to force times distance. 

So let's say he moves the long end of the lever by 1 foot. The total
work is 50 lbs times 1 foot, or 50 ft-lbs.  

How far will the other end of the lever travel? You can use similar
triangles to figure that out. Whatever it turns out to be, the work
on each side, 

  force * distance = force' * distance'

will have to be the same. So if you know force, distance, and 
distance', you can use that to find force'... which will tell you how
much you can lift. 

Does that make sense? 

- Doctor Ian, The Math Forum
  http://mathforum.org/dr.math/