Question:
A river 2 m deep and 45 m wide is flowing at the rate of 3 km/h. Find the quantity of water that runs into the sea per minute.
Solution:
Area of the cross-section of river $=45 \times 2=90 \mathrm{~m}^{2}$
Rate of flow $=3 \mathrm{~km} / \mathrm{hr}=\frac{3 \times 1000}{60}=50 \frac{\mathrm{m}}{\mathrm{min}}$
Volume of water flowing through the cross-section in one minute $=90 \times 50=4500 \mathrm{~m}^{3}$ per minute