The figure shows 2 tanks, Tank L and Tank M. Tank M is completely empty while Tank L is filled with water to the brim. Water from Tap K flows in at a rate of 3.6 litres per minute while water drains from Tap J at a rate of 2.16 litres per minute. Both taps are turned on at the same time. After some time, the heights of the water level in both tanks became the same.
- Find the time taken for the heights of the water level to be the same in both tanks.
- Find the height of the water level at that point of time.
(a)
Base area of Tank L
= 30 x 25
= 750 cm
2 1 ℓ = 1000 cm
3 3.6 ℓ = 3600 cm
3 2.16 ℓ = 2160 cm
3 Height increase per minute for Tank L
= 3600 ÷ 750
= 4.8 cm/min
Base area of Tank M
= 40 x 20
= 800 cm
2 Height decrease per minute for Tank M
= 2160 ÷ 800
= 2.7 cm/min
Let t be the time taken for both the water levels to become the same.
4.8 t = 12 - 2.7 t
7.5 t = 12
1 t = 1.6 min
(b)
Height of the water level
= 4.8 t
= 4.8 x 1.6
= 7.68 cm
Answer(s): (a) 1.6 min; (b) 7.68 cm