[noork85]

hi, i cant figure out how to go about doing this problem. a step by step ans would be real helpful.

How much thermal energy is required to heat all of the water in a swimming pool by 1.0 degrees C if the dimensions are 4.0 ft deep b 20. ft wide by 75 ft long? Answer is in MegaJoules.

i know the formula to find thermal energy is cmT. the book has the ans as 1.0 x 10^2kj
how do they get that ans? i assumed my ans would involve multiplication with the C of water which is 4.184J-g-C.

any help is appreciated.

[Borek]

Calculate mass of water in the pool.

[noork85]

a little bit more info, please. i wouldnt ask if i knew...im clueless.
i multiplied the dimensions and got 6000ft. what next?

[Borek]

What is a density of water? How are density, mass and volume related?

[sjb]

a little bit more info, please. i wouldnt ask if i knew...im clueless.
i multiplied the dimensions and got 6000ft. what next?

No, you did not get 6000 ft. As well as the numbers, you need to multiply units as well.

[noork85]

i converted the 6000ft to cm and got 182800cm^3.
i plugeed that into the density formula and got 182,880g

the change in temp is what i dont know. it just says its raised by one degree.

what do i do next? my exam is tomorrow and desperately need help, if smeone can just help out? thanks!

[noork85]

is the ans even correct? the one the book has stated?

[Borek]

i converted the 6000ft to cm and got 182800cm^3.

1 cubic feet is not 30.48 cubic cm.

1 feet is 30.48 cm, so 1 cubic feet is 30.48³ cm³.

[noork85]

what do i do? can u please just tell me? im at an absolute loss.

[dipesh747]

Right well start off by converting your units of distance from feet into meters. (1 foot = 0.3048m)
After you have done that you can use the equation Density = mass x volume

Density of water is 1000 Kg / m3

So if you divide density by volume (which you can do bcz the units will be (Kg/m3)/(m3) you obtain mass in...(Kg) Remeber, you can only divide units when they are the same! so always make sure they are.

Right so now you have you mass you can use the equation you stated

Thermal E = heat capacity (units?) x mass x change in temp

your heat capacity is in J/g/c your mass is in Kg and you temp is in c

So you need to change J/g/c into J/Kg/c so you can multiply your heat capacity by your mass.

To do this multiply 4.184 by 1000

Then you need to convert your answer into KJ...so how do you convert J into KJ.....I'm sure you can figure that one out yourself!

[Arkcon]

what do i do? can u please just tell me? im at an absolute loss.

Well, you initially said:

i know the formula to find thermal energy is cmT. the book has the ans as 1.0 x 10^2kj

Can you plug in the values you have for the correct variables in your formula?  Once you have thme in a line, like that, with the units for each value you have, you'll be able to see what you're missing, and what needs to be converted to another unit.  If you do the conversion wrong, you can correct it, and change it in your formula, and see if you get the correct answer.