(18) The external surface of an iron pipe oflength 70 cm is painted fo

1.	(18) The external surface of an iron pipe oflength 70 cm is painted for 2800. If therate of painting is 25 per sq.cm, find theradius and the volume of the pipe (correctto two places of decimal).
Answer» Dimensions of a Iron pipe: Length of the pipe (H) = 70 cm $Cost \: of \: painting\: external \: surface\\of \: the \: pipe = C.S.A \: of \: cylinder = Rs\: 2800$ $Let \: radius \: of \:the \:pipe = r \:cm$ /* ACCORDING to the problem GIVEN */ $1 \: square \:cm \: painting \: Cost \: Rs \:25 \\Now, Area \: of \: painting \: external \:surface \\of \:the \:pipe = \frac{2800}{25} = 112 \: cm^{2}$ $\boxed { \pink { CSA \: of \: a /: cylinder = 2\pi rh }}$ $\implies 2\pi rh = 112$ $\implies 2 \times \frac{22}{7} \times r \times <klux>70</klux> = 112$ $\implies r = \frac{ 22\times 7}{2 \times 22\times 70 } \\= 0.25 \:cm$ $Volume \: of \:the \:pipe (V) = \pi r^{2} h \\= \frac{22}{7} \times (0.25)^{2} \times 70 \\= 13.75 \:cm^{3}$ THEREFORE., $\red { Radius \: of \:the \:pipe }\green {= 0.25\:cm }$ $\red { Volume \: of \:the \:pipe }\green {= 13.75\:cm^{3} }$ •••♪

(18) The external surface of an iron pipe oflength 70 cm is painted for 2800. If therate of painting is 25 per sq.cm, find theradius and the volume of the pipe (correctto two places of decimal).

Answer»

Dimensions of a Iron pipe:

Length of the pipe (H) = 70 cm

$Cost \: of \: painting\: external \: surface\\of \: the \: pipe = C.S.A \: of \: cylinder = Rs\: 2800$

$Let \: radius \: of \:the \:pipe = r \:cm$

/* ACCORDING to the problem GIVEN */

$1 \: square \:cm \: painting \: Cost \: Rs \:25 \\Now, Area \: of \: painting \: external \:surface \\of \:the \:pipe = \frac{2800}{25} = 112 \: cm^{2}$