485. Water is flowing at the rate of 0.70 m/sec through a circular pipe, whose internal diameter is 2 cm into a cylindrical tank the radius of whose base is 40 cm. Determine the increase in the water level in 1/2 hour.

Let R m be the radius and H m be the height of a circular pipe, then

            

[length of water column = Height of circular pipe]
Volume of water that flow's out of the circular pipe in 1 sec
= πR²H
= π x 0.01 x 0.01 x 0.70
= 0.00007 π m³.
Therefore, Volume of water that flows out of
the circular pipe in  hr (30 x 60) sec
                    = (0.00007  x 1800) cm³ 
                    = 0.126 
Let r m be the radius and h m be the height of cylindrical tank, then
r = 40 cm =  = 0.4 m, h = ?
Now, Volume of water in the cylindrical lank up to a height of h m
= πr²h =  π x 0.4 x 0.4 x h = 0.1 6π h m².
Since, Volume of the water flown into the tank
= Volume of the water that flows through the pipe in half an hour.
⇒ 0.16 π h = 0.126 π


Hence, increase in water level in 1/2 hr = 7875 m.