Solving Lever Calculations to Help Son

• Alan Butcher
In summary, the conversation involves a person seeking help to determine the distance from the end of a 5m lever to the fulcrum, in order to balance a weight of 300kg with a force of 100kg. The solution involves understanding the torques involved in a lever and using the formula F1D1 = F2D2, where F is the force and D is the distance from the fulcrum. The additional hint is given to consider that the two distances must add up to 5m and to use this information to solve for the unknown distances.

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?

Can you assist please?

I feel there must be some better formula.

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?

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

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

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.