RRB RPF RPSF SI and CONS Model Papers 3 with solutions

(d) Internal diameter of the tube = 6 cm
∴ Internal radius (r) = 3 cm
Height of the tube (h) = 10 cm
Thickness of the metal = 1 cm
∴ Outer radius (R) = Thickness of the metal +Internal radius = 1 + 3 = 4 cm
∴ Outer curved surface area $=2\mathrm{\pi }\mathit{r}\mathit{h}+\mathrm{\pi }{\mathit{R}}^2+\mathrm{\pi }\left({\mathit{R}}^2-{\mathit{r}}^2\right)$
$=2\mathrm{\pi }\left(3\right)\left(10\right)+\mathrm{\pi }{\left(4\right)}^2+\mathrm{\pi }\left(16-9\right)$
$=60\mathrm{\pi }+16\mathrm{\pi }+7\mathrm{\pi }=83\mathrm{\pi }\mathrm{sq}\mathrm{cm}$