A heavy boy and a lightweight girl are balanced on a massless seesaw. If they bo

Question

A heavy boy and a lightweight girl are balanced on a massless seesaw. If they both move forward so that they are one-half their original distance from the pivot point, what will happen to the seesaw? Assume that both people are small enough compared to the length of the seesaw to be thought of as point masses. It is impossible to say without knowing the masses. It is impossible to say without knowing the distances. The side the boy is sitting on will tilt downward. Nothing will happen; the seesaw will still be balanced. The side the girl is sitting on will tilt downward.

Explanation / Answer

D). Nothing will happen; the seasaw will still be balanced.

Explanation:- For this situation to be true, we must have

(M * R) / (m * r) = 1

where
M = mass of boy
R = distance boy is from center

m = mass of girl
r = distance girl is from center

Halving each distance...

(M * R / 2) / (m * r / 2) = ½ (M * R) / ½ (m * r)

The ½'s will cancel, leaving us

(M * R) / (m * r)

But we know this is 1, so they will still be in balance.

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