helping me find the correct answer!!

Question

adunb8 · Answer

100 psi (5ft^3) and -20 BTU 
 I have no idea how the answer is 72.5 BTU. ..

adunb8 · Answer

i've tried many ways but it still doesn't come out.. 
i have to add -20btu to (100psi x 5ft^3)

jskhupmang · Answer

this sound physic to me

adunb8 · Answer

i know it has to do with conversion stuff but how do i do it... how do i make them all into 1 unit conversion?

jskhupmang · Answer

anyway btu = 1055 joules

jskhupmang · Answer

multiply is the key in any kind of conversion

adunb8 · Answer

and 1 psi = 6.894 kpa which 1 kpa = 1x10^5 N/m^2

jskhupmang · Answer

Im not a smartass but I'll try :)

adunb8 · Answer

thank you~!

jskhupmang · Answer

psi means pound per square inches right?

adunb8 · Answer

yes

adunb8 · Answer

so i got 689.4 kPa for 100 psi

jskhupmang · Answer

i got -21100 juoules for -20 btu

adunb8 · Answer

and then 689.4 x (1x10^5 N/m^2) then how do i multiply 5ft^3? is there conversion involved here?

adunb8 · Answer

@jskhupmang i got that too~

anonymous · Answer

psi, lbf/in2  you cant multiply by ft you need to convert ft to in

jskhupmang · Answer

oh ok so 12 inch = 1ft

jskhupmang · Answer

and 60 inches then?

adunb8 · Answer

but it is ft^3

jskhupmang · Answer

but we need to cube it right

jskhupmang · Answer

so 60^3=216000

jskhupmang · Answer

216000ft^3

adunb8 · Answer

yes thats what i got

jskhupmang · Answer

summary we have got: 
689.4 kPa = 100 psi 
 -21100 juoules = -20 btu
5ft^3 = 216000inches^3

adunb8 · Answer

then i converted 689.4 kPa to 689.4 x 10^5 to be N/m^2

jskhupmang · Answer

so what do we do next? do we just multiply them all?

jskhupmang · Answer

or do have the formula so we can plug them in

adunb8 · Answer

i am not sure.. but the answer is 72.5 BTU so we probably need to convert them back to BTU

adunb8 · Answer

@Mertsj this is the problem =(

mertsj · Answer

So you want to multiply 100 psi by 5 cubic feet and subtract 20 BTU's and get 72.5 BTU's?

jskhupmang · Answer

can you just help us how to convert it?

adunb8 · Answer

basically

mertsj · Answer

Convert what to what?

jskhupmang · Answer

idk lol but do you know how to derive the answer (72.5 BTU's)?

mertsj · Answer

I have to think about it.

adunb8 · Answer

bascially we want to do -20BTU to (100psi x 5ft^3) to get 72.5 BTU

adunb8 · Answer

but we are stuck on conversions..

mertsj · Answer

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