Question

water is flowing through a cylindrical pipe of internal diameter 2 cm into cylindrical tank of base radius 40 cm at the rate of 0.4 metre per second determine the rise in level of water and the tank in half an hour

Answer 1

See the volume of water which passes through the cylindrical pipe is equal to the volume of water present in the cylindrical tank after half an hour. 

So volume will remain conserved. 

For cylindrical pipe
Radius 0.01m
Height 0.4m/s ie 0.4*60*30m In half an hour. 

For cylindrical tank
Radius 0.4m
Height x(let) 

V1=V2
3.14*(0.01)^2*720=3.14*(0.4)^2*x

Solving for x 
We get x=45cm.