Question

$748$ cc of metal is used to make a metallic cylindrical pipe of length $14$ cm and external radius $9$ cm. Find its thickness.

• A. $2$ cm
• B. $2.5$ cm
• C. $1.5$ cm
• D. $1$ cm

Answer 1

The correct option is D $1$ cm

Volume of the metallic cylindrical pipe$=748cc=748{cm}^3$
Length of the cylindrical pipe, $h=14cm$
External radius of the pipe,$R=9cm$
Let the internal radius of the cylindrical pipe be ${}^{\prime }{r}^{\prime }cm$
Therefore the volume of the metallic pipe$=\pi (R^2-r^2)h$
$\Rightarrow \frac{22}{7}(9^2-r^2)\times 14=748\Rightarrow 44(81-r^2)=748$
$\Rightarrow 81-r^2=\frac{748}{44}=17\Rightarrow r^2=81-17=64$
$\Rightarrow r=\sqrt{64}=8cm$
Therefore, thickness of metallic pipe$=R-r=9-8=1cm$