Question:
A river 3m deep and 40 m wide is flowing at the rate of 2 km per hour. How much water will fall into the sea in a minute?
Solution:
Radius of the water flow = 2 km per hour = (2000/60) m/min
= (100/3) m/min
Depth of the river (h) = 3 m
Width of the river (b) = 40 m
Volume of the water flowing in $1 \mathrm{~min}=100 / 3 * 40 * 3=4000^{3}$
Thus, 1 minute $4000 \mathrm{~m}^{3}=4000000$ litres of water will fall in the sea.