The length of canvas 1.1 m wide required to build a conical tent of height 14 m and the floor area 346.5 sq.m is :

Answer: Option B

$$\begin{array}{rl}& \pi r^2=346.5\\ & r^2=\left(346.5\times \frac{7}{22}\right)\\ & r^2=\frac{441}{4}\\ & r^2=\frac{21}{2}\\ & \therefore l=\sqrt{r^2+h^2}\\ & =\sqrt{\frac{441}{4}+{\left(14\right)}^2}\\ & =\sqrt{\frac{1225}{4}}\\ & =\frac{35}{2}\end{array}$$
So, area of canvas needed :
$$\begin{array}{rl}& \pi rl=\left(\frac{22}{7}\times \frac{21}{2}\times \frac{35}{2}\right){\text{m}}^2\\ & =\left(\frac{33\times 35}{2}\right){\text{m}}^2\end{array}$$
∴ Length of canvas :
$$\begin{array}{rl}& =\left(\frac{33\times 35}{2\times 1.1}\right)\text{ m}\\ & =525\text{ m}\end{array}$$