# Lever calculations

1. Mar 12, 2007

### Alan Butcher

My problem (trying to help an ay last keen son)-a lever 5m long, a weight of 300kg, a force of 100kg.
The question says describe?

I am trying to work out the distance from the end of lever to fulcrum

or in other words where the fulcrum should lie.

tried formula which has gone to course with son but it gives L over little l = force over effort?

I feel there must be some better formula.

2. Mar 12, 2007

### Staff: Mentor

Look at the torques involved in a lever. To be in balance about the fulcrum, the torques must be equal. In other words:
$$F_1 D_1 = F_2 D_2$$

where the Fs are the two forces applied to the lever and the Ds are the distances from the fulcrum. You are given the forces. Hint: What must those two distances add to?

3. Mar 12, 2007

### Alan Butcher

ah ha these two Ds add up to my 5m lever right?

ok

F1D1 = F2D2

but D1+D2 = 5m

so

mmm
after 45 years away from school

Last edited: Mar 12, 2007
4. Mar 12, 2007

### Alan Butcher

If in the above formula I know that D1 and D2 add up to 5m how do I find what D1 and D2 are?

5. Mar 12, 2007

### hage567

If you know both distances add up to 5m, you can say one is D1, and the other must then be D2=5-D1. Put that into your equation and you can solve for D1.