Speed of water = 2.52 kmph = 2520 m/hr
Length, h’ = 2520 m
Let the radius of the pipe be r’ and radius of the tank, r’’ = 40 cm = 0.4 m
Level of water in the tank in half and hour = 3.15 m
Level of water in the tank in an hour, h’’ = 6.30 m
Now,
the volume of pipe = volume of the tank
⇒ πr’2 h’ = πr’’2 h’’
⇒ r’2 (2520) = (0.4)2 (6.3)
∴ diameter = 2r’ = 2 × 2 = 4 cm