Question

An iron pipe is $42$ cm long and its experior radius is $4$ cm If the thickness of the pipe is $1$ cm and iron weights $100g/c{m}^3$ the weight of the pipe is

• A. $92.4$ kg
• B. $118.8$ kg
• C. $211.2$ kg
• D. $189.34$ kg

Answer 1

Answer: (B)

The correct option is D $118.8$ kg
$l=42$ cm $r=4$ cm thickness$=1$ cm weight of iron$=100g/c{m}^3$
Volume of cylinder$=\pi r^{2}h$
$\therefore$ Volume of iron pipe=$\pi {(4+1)}^{2}42-\pi \times 4^2\times 42$
=$\pi \times 42(25-16)$
=$\frac{22}{7}\times 42\times 9=1188c{m}^3$
Weight of 1 $c{m}^3$ iron$=100g$
$\therefore$ Weight of 1188 $c{m}^3$ iron$=1188$$\times$ $100=118800g=118.8kg$