Question

A rectangular water tank measures 2.4m long, 2m wide and 1.5m high. The tank contained some water up to a height of 0.45m

(a) calculate the amount of water, in litres, needed to fill up the tank.
vol = 2.4*2* 1.5- 2.4*2*0.45
=7.2 - 2.16
= 5.04*1000
= 5040L
(b) An inlet pipe was opened and water let to flow into the tank at a rate of 10 litres per minute. After one hour, a drain pipe was opened and water allowed to flow out of the tank at a rate of 4 litres per minute.

(i) the height of water in the tank after 3hours

(ii) the total time taken to fill up the tank

Answer 1

empty space volume is 2.4*2*(1.5-0.45) = 5.04 m^3 = 5040L
you are correct

So, initially, there were 2.16 m^3 = 2160L in the tank
during the first hour, 10L/min * 60min = 600L flowed into the tank.

when the valve was opened, the net fill rate was 10-4 = 6L/min

volume after 3 hours was 600 + 6*2*60 L
total minutes to fill was 60 + (5040-600)/6 minutes

Answer 2

0.68m