# Homework Help: To find the density of a material of the body using moments

1. Jul 25, 2009

### leena19

1. The problem statement, all variables and given/known data
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Fig.A shows the balanced position of a light rod carrying an object X and a mass M .
Fig.B shows the balanced position of the same system when X is immersed in water.If the density of water is d,the density of the material made of X is given by,
1) [L[SUB]1[/SUB]/(L[SUB]1[/SUB]-L[SUB]2[/SUB])]d 2) (L[SUB]1[/SUB]/L[SUB]2[/SUB])d 3) [L[SUB]1[/SUB]/L[SUB]1[/SUB]+L[SUB]2[/SUB]]d 4) [(L[SUB]1[/SUB]-L[SUB]2[/SUB])/L1]d 5) (L[SUB]2[/SUB]/L[SUB]1[/SUB]) d

[b]2. Relevant equations[/b]

[b]3. The attempt at a solution[/b]
for A
mg*l = Mg*L[SUB]1[/SUB]
m=ML[SUB]1[/SUB]/l m=mass of X

for B
Mg*L[SUB]2[/SUB] = m[SUB]1[/SUB]g*l
m[SUB]1[/SUB]= ML[SUB]2[/SUB]/l m[SUB]1[/SUB]g = apparent weight of X in water

density of X= (real weight/apparent loss of weight in water) d
=(m/m-m[SUB]1[/SUB])*d
=(1-m/m[SUB]1[/SUB])d
=(1-L[SUB]1[/SUB]/L[SUB]2[/SUB])*d
gives me( L[SUB]2[/SUB]-L[SUB]1[/SUB]/L[SUB]2[/SUB])*d, which is not even among the choices given.
I can't figure out where I'm going wrong.

Last edited by a moderator: Apr 24, 2017
2. Jul 25, 2009

### alphysicist

Hi leena19,

Last edited by a moderator: Apr 24, 2017
3. Jul 25, 2009