Discovering the Mass of an Object on a Ruler Using Known Variables - Find M_2

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To find the unknown mass M_2 using the known mass M_1 and the distances L_1 and L_r, the equation M_1*L_1 = M_2*L_2 is used, where L_2 is the distance from the pivot to the end of the ruler. The correct expression for L_1 should be adjusted to L_1 = L_1 - 0.5*L_r, and L_2 is determined as 0.5*L_r. The initial attempt at the solution was incorrect, leading to confusion about the proper setup of the equation. Clarifying the distances and correctly applying the lever principle will yield the correct mass M_2 in terms of M_1, L_1, and L_r. Understanding these relationships is crucial for solving the problem accurately.
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Homework Statement


We have a ruler with a total length L_r and a pivot at its middle. An object of known mass M_1 is placed a distance L_1 from the end of the ruler, as shown. An object of unknown mass M_2 is placed at the end of the ruler.

http://session.masteringphysics.com/problemAsset/1010957/18/MFS_to_6_b.jpg

Find the mass M_2.
Express the mass in terms of M_1, L_1, and L_r.


Homework Equations



M_1*L_1 = M_2*L_2

The Attempt at a Solution


i tried doing ((M1)*0.5*(Lr)) / (L1 - 0.5Lr) but that's wrong and i don't understand why...
 
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channel1 said:
M_1*L_1 = M_2*L_2

The Attempt at a Solution


i tried doing ((M1)*0.5*(Lr)) / (L1 - 0.5Lr) but that's wrong and i don't understand why...

L_1 is L1-0.5Lr and L_2 is 0.5*Lr
 

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