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

F_1*d_1=F_2*d_2

In our case:
F_1*d_1=F_2*d_2
d_2=(F_1*d_1)/F_2
d_2=(5kg*6m)/(3kg)
d_2=10m

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