Solution:

Given speed of water flow = 15 km/h

Diameter of pipe = 14 cm

So radius of pipe, r = 14/2 = 7 cm = 0.07 m

Dimensions of cuboidal pond = 50 m × 44 m

Height of water in pond = 21 cm = 0.21 m

So volume of water in pond = 50×44 ×0.21

= 462 m³

Volume of water in pipe = r²h

= ×0.07²×h

= 0.0049h

Volume of water in pond = Volume of water in pipe

462 = 0.0049h

h = 462/0.0049

= 462×7/0.0049×22

= 30000 m

= 30 km [1 km = 1000 m]

Speed = distance/ time

Time = Distance/speed = 30/15 = 2 hr

Hence the time taken is 2 hours.