Question

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

Answer 1

Answer: 0.14

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