Question

You are given a sphere of radius 2 cm. If you are asked to select a best suited spring balnce to determine its weight, then out of the following which one would you prefer? The sphere is made of an alloy of density $7\times {10}^{3}kg{m}^{-3}$.

Answer 1

Given:
Radius of the sphere, r =2 cm =0.02 m
Density of alloy, $d=7\times {10}^{3}kg{m}^{-3}$
density $=\frac{mass}{volume}$
mass, $m=density\times volume=7\times {10}^3\times \frac{4}{3}\pi r^3$
$m=7\times {10}^3\times \frac{4}{3}\times 3.14\times (0.02{)}^{3}m=234.43\times {10}^{-3}kg=234.34gwt$
We can take the range of the weight around 0-250 gwt. So if we consider a balance spring balance with this range its least count will be 2.5 gwt.