# Homework Help: Mechanical properties of matter problem,

1. Feb 22, 2010

### StudentPhys

Mechanical properties of matter problem, urgent!!!

1. The problem statement, all variables and given/known data
When a beaker partially filled with water is placed on an accurate scale, the scale reads 22g . If a piece of metal with density 3800 kg/m^3 and volume 2,4 cm^3 is suspended by a thin string so that the metal is submerged in the water but does not rest at the bottom of the beaker, what does the scale read?

2. Relevant equations

Fnet=0
Fb= mg-Fs
N(y) + Fs(Y)+mg(-y)+(22*g)(-y)=0

3. The attempt at a solution
V=2,4cm^3=2.4*10^-6 m^3 density= 3800 kg/m^3
mass metal= 0,00912 [kg]
System Metall: Fs+ Fb+ mg= 0
Fb= mg-Fs
System: Beaker + Metall+ H20
System : Beaker + metall + h20
N(y) + Fs(Y)+mg(-y)+(22*g)(-y)=0
N= 22*g+ Fb
solving for N= 9.8 / 24.4*10^-3)

Is this the right way of solving the problem? Are there other methods-easier? In that case please let me know, asap i have a crucial-grade determining -test in 2 days!!!

Btw , another question, how come in the equation for the Bigger system , one disregards the buoyancy force but then is allowed to plug it in ?
Thanks in advance

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