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# maths question

ok so you have a hot water cylinder with a radius of 20cm and a height of 120cm, what is the volume of the cylinder in cubic centimetres using the formulas pi R2h

and pi being 3 not the 3.14.

????

and pi being 3 not the 3.14.

????

Volume of a cylinder is the area times the height. Area is pi times the square of the radius.

So volume = 3 x (20 x 20) x 120 = 3 x 400 x 120 = 144,000cm^3

3x400x120

144,000 cm3 (cubed)

Original Poster

pi is 3.142 or to be pricise 3.14159265 so when i said 3.142 that was pi rounded to 3 decimal places.

Edited by:"shamus1975" 15th Nov 2010Original Poster

one cubic centimetre of water weighs 0.001kg. so when the cylinder is full what will the water weigh in KG's.

^^^^^This^^^^^

Can you seriously not work this out yourself???

Depends. 1ml of water only weighs one gramme at 4 degrees Celcius. This is a hot water tank, so the water will have expanded and have a lower overall density.

So we need to know the temperature of the water in the tank and also whether the volume of the tank is measured when cold or hot.

Actually, no. STP is either 0C or 20C and the water wouldn't weigh 144kg at either of those.

In fact, there are many definitions of STP but none of them involve 4 Celcius.

Edited by:"ro53ben" 15th Nov 2010Quite so, but since you and the original poster are using

massandweightas synonymous and the OP is taking Pi as3, 144 is a good enough approximation.Edited by:"cannyscot" 15th Nov 2010Agreed

Original Poster

yes cant you its just a bit of afternoon trivia i noticed you never answered

Edited by:"shamus1975" 15th Nov 2010Original Poster

yeah just a question we set in a quiz, did not think of the temperture coming into effect, lets hope we dont get some clever person answering lol.

well done any ways.

Original Poster

its simplified for a pub quiz, its a bit of fun not a real life renovation product