Question

A scale reads 398 N when a piece of copper is hanging from it. What does it read (in N) when it is lowered so that the copper is submerged in water?

Answer 1

$mass_{copper} = w/g=398/9.8=40.6122kg$

$density \space of \space copper=8960kg/m^3$

$V_{copper}=mass/density=40.6122/8960=4.5326\times 10^{-3}$ $m^3$

upthrust force $=density\space of \space water \times volume \times gravity=1000\times4.5326\times10^{-3}\times 9.8=44.4195N$

scale reading$=398N-44.4195N=353.58N$