Question

The radius of a uniform wire is $r =0.21\, cm$. The value of $\pi$ is given to be $\frac{22}{7}$. What is the area of cross section $\left(\right.$ in $\left.cm ^{2}\right)$ of the wire upto correct significant figures?

Answer 1

Area, $A =\pi r ^{2}=\frac{22}{7} \times(0.21)^{2}=0.1386\, cm ^{2}$
There are only two significant figures in $0.21\, cm$.
Hence the result must be rounded off to two significant figures
i.e., $A =0.14\, cm ^{2}$.