Question

A spring balance read 10 kg when a pail of water is suspend from it. What be its reading when (a) an ice cube of mass 1.5 kg is put into the pail , (b) an iron piece of mass 7.8 kg suspended by another string immersed with half its volume inside the water in the pail. Relative density of iron is 7.8

Answer 1

A spring balance reads weight of the object ranged in it .

weight of pair water is thus $=mg$

$\Rightarrow W_o=10\times 9.8=98N$ $(g=9.8m/s^2)$

$\left(i\right)$

When is ice of man $=1.5kg$ is immersed , its weight adds up

$\Rightarrow$ Reading of balance $=W_o+mg$

$=98+1.5\times 9.8=112.7N$

In this case the spring measures apparent weight of the iron piece apparent weight.

$W^{\prime }=W-F_b$

$=Vpg-\frac{V}{2}pg$ [V:volume of iron ]

p:density

$\Rightarrow W^{\prime }=\frac{V}{2}pg=\frac{Mg}{2}$ $[M=PV]$

$=\frac{7.8\times 9.8}{2}=38.22N$