Question

A rectangular reservoir is 120m long and 75m wide . At what speed per hour must water flow into it through a square pipe of 20cm wide so that the water rises by 2.4m in 18hours?

Answer 1

Your answer will be

Is the 1.5

Answer 2

Answer:

We have,

Volume of water accumulated in the reservoir in 18 hrs.

= (120×75×2.4) m³

________________________

Let the speed of the water be v km/hr

Clearly, water in the pipe forms a cuboid of width ..

$\sf \frac{20}{100} = \sf \frac{1}{5} m \\ \\ \sf height = \frac{20}{100} = \sf \frac{1}{5} \: m$

Length of the water cuboid formed in 18 hrs = 18v km = 18000v metres.

$\therefore$ volume of water accumulated in the reservoir in 18 hrs

$\sf = 18000v \times \frac{1}{5} \times \frac{1}{5} {m}^{3} = \sf720v \: {m}^{3} \\ \\ \ \sf from \: (i) \: and \: (ii), \: we \: have \\ \\ \sf 720v = 120 \times 75 \times 2.4 \\ \\ =\sf v = \frac{120 \times 75 \times 2.4}{720} = \sf30km/hr$