A balanced lever has two weights on it, the first with mass 5kg and the second with mass 3kg. If the first weight is 6m from the fulcrum, how far is the second weight from the fulcrum?

1 Answer
Walker P
Feb 25, 2017

10 meters

Explanation:

Imagine a see-saw where two people sit on either end.
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Assuming the two smileys weigh the same amount and are the same distance from the center of the see-saw (the fulcrum), the see-saw is balanced.

Now imagine, the pink smiley and her best friend sit together on her end of the see-saw. What happens? The pinks' side will go down, while the boy's side goes up!
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Next, let's say the pink's scoot up the see-saw so that they are sitting half-way between the end of their side and the fulcrum. What happens now?
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They're balanced again! So, we've changed two variables: weight and distance. The ability to rotate around a fulcrum, torque, is dependent on force and distance.

If a system is not rotating, clockwise and counter-clockwise rotation are balanced:

F1⋅d1=F2⋅d2

In our case:
F1⋅d1=F2⋅d2
d2=F1⋅d1F2
d2=5kg⋅6m3kg
d2=10m

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