this is the correct answer
Given, internal diameter of cylindrical pipe = 2 cm
So, radius of cylindrical pipe (r) = 2/ 2 = 1 cm
Area of cross section of pipe= r2= (1)2= cm2
Speed of water= 0.4 m/s =0.4 x 100 cm/s = 40 cm/s
Volume of water flown out in half an hour = x 40 x 30 x 60 = 72000 cm2
Radius of cylindrical tank (R) = 40 cm
Let level of water rise to the height of h cm.
Volume of cylindrical tank = R2h = (40)2h = 1600h cm2.
Volume of cylindrical tank = Volume of water flown out in half an hour
1600h = 7200
h = 45cm
Hence, level of water rise to the height of 45 cm.
Hope it helps