This is one of the most important question from the cbse board exam point of view because in 2012 and 2009 cbse board exam this question was asked. Question number 20 from RS Aggarwal book page number 811 , exercise 17B, chapter volume and surface area of solid.
Deepak BoraNewbie
A hemispherical tank, full of water, is emptied by a pipe at the rate of 25/7 litres per second. How much time will it take to empty half the tank if the diameter of the base of the tank is 3 m?
Share
Given,
Diameter = 3m = 300 cm
radius( r) = 300/2 cm = 150 cm
Volume of water = volume of hemisphere = [2/3] π r³
= [2/3] * π * 150*150*150
Half of the volume = (1/3 * π * 15 * 15 * 15 * 1000) cm³
= (2475 * 10^4) /7 cm³
Since 1000 cm³ = 1 litre
= (2475*10^4) /7 cm³
= 2475*10^4) / 7000
= 24750/7 litre
Since , 25/7 litre is emptied in 1 second
24750/7 litre will be emptied in(24750*7)/25*7 seconds
=990 seconds
= 16 min 30 sec