**Question:**

In a hospital, used water is collected in a cylindrical tank of diameter 2 m and height 5 m. After recycling, this water is used to irrigate a park of hospital whose length is 25 m and breadth is 20 m. If the tank is filled completely then what will be the height of standing water used for irrigating the park? Write your views on recycling of water.

**Solution:**

Diameter of cylinder (*d*) = 2 m

Radius of cylinder (*r*) = 1 m

Height of cylinder (*H*) = 5 m

Volume of cylindrical tank, $\mathrm{V}_{c}=\pi r^{2} H=\pi \times(1)^{2} \times 5=5 \pi \mathrm{m}$

Length of the park (*l*) = 25 m

Breadth of park (*b*) = 20 m

height of standing water in the park = *h*

Volume of water in the park $=l b h=25 \times 20 \times h$

Now water from the tank is used to irrigate the park. So,

Volume of cylindrical tank = Volume of water in the park

$\Rightarrow 5 \pi=25 \times 20 \times h$

$\Rightarrow \frac{5 \pi}{25 \times 20}=h$

$\Rightarrow h=\frac{\pi}{100} \mathrm{~m}$

$\Rightarrow h=0.0314 \mathrm{~m}$

Through recycling of water, better use of the natural resource occurs without wastage. It helps in reducing and preventing pollution.

It thus helps in conserving water. This keeps the greenery alive in urban areas like in parks gardens etc.