A river 3 m deep and 40 m wide is flowing at the rate of 2 km per hour.

Solution:

Rate of water flow = 2 km per hour

$=\left(\frac{2000}{60}\right) \mathrm{m} / \mathrm{min}$

$=\left(\frac{100}{3}\right) \mathrm{m} / \mathrm{min}$

Depth (h) of river = 3 m

Width (b) of river = 40 m

Volume of water flowed in $1 \mathrm{~min}=\left(\frac{100}{3} \times 40 \times 3\right) \mathrm{m}^{3}=4000 \mathrm{~m}^{3}$

Therefore, in 1 minute, $4000 \mathrm{~m}^{3}$ water will fall in the sea.