# Ex.13.2 Q6 Surface Areas and Volumes - NCERT Maths Class 9

## Question

Curved surface area of a right circular cylinder is \(4.4\) \(\begin{align}\rm{{m^2}}. \end{align}\). If the radius of the base of the cylinder is \(0.7 \,\rm{m},\) find its height.

## Text Solution

**Reasoning:**

The curved surface area of a right circular cylinder of the base radius \(r\) and height \(h\) is \(\begin{align}2\pi rh. \end{align}\)

**What is the known?**

Curve surface area and radius of the base.

**What is the unknown?**

Height of the cylinder.

**Steps:**

Curved surface area \(\begin{align}2\pi rh \end{align}\)\(=\) \(4.4\)\(\begin{align}\rm{{m^2}} \end{align}\)

\[\begin{align}\rm radius(r) &= 0.7m\\\rm height(h) &= ? \end{align}\]

\[\begin{align}2\pi rh &= 4.4\\2 \times \frac{{22}}{7} \times 0.7 \times h &= 4.4\\h &= \frac{{4.4 \times 7}}{{2 \times 22 \times 0.7}}\\\,\,\,\,\, &= 1\,\,\rm{m} \end{align}\]

The height of the right circular cylinder is \(\begin{align} = 1\,\rm{m} \end{align}\).