Question

A hollow cylinder of negligible thickness and radius $r$ is mounted by a hollow hemisphere of the same radius. The height of the cylinder is $h$. If the solid formed is to be painted . What is the total surface area that has to be painted?

• A. $2\pi rh+4\pi r^2$
• B. $2\pi rh+\pi r^2$
• C. $2\pi rh+3\pi r^2$
• D. None of the above

Answer 1

The correct option is C $2\pi rh+3\pi r^2$

Total surface area painted to be $=$ curved surface area of cylinder $+$ curved surface area of hemisphere $+$ area of base circle of cylinder
$A=2\pi rh+2\pi r^2+\pi r^{2}A=2\pi rh+3\pi r^2$