PHYSICS How would I tackle this?

I'm getting very confused I think there is a formula I don't know about. Can someone help me with the theory?





Q: The surface area of the skin i 1.8m^2


Heat is lost at a rate of 100 Watts per 1m^2 at 10deg cel.


How much will the body loose in a day.





My answer:


If 100 W per second (i.e. W = J/s)


then 100/(60x60) = 0.028 W/h


x 24 for whole day is 0.672 per 1 meter^2


So 0.672 x 1.8 = 1.2096 J





If I am wrong (which I suspect I am) please include theory so I can learn!


THANKS x

PHYSICS How would I tackle this?
For each second heat lost is 100 Joule per m^2





For one hour heat lost is 100 x 60 x60. per m^2





For 1 day heat lost is 100 x 60 x60 x 24.per m^2.





For 1.8m^2 heat lost is 100 x 60 x60 x 24 x 1.8.





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Reply:You have errors in units and divided where you should have multiplied.





If 100 J per second per m² (i.e. W = J/s)





then 100J/s/m² * (60 s/min x 60 min/hr) = ____ J/m²/hr





x 24 hr for whole day is ____ J per meter²


.


.


.





Try keeping your units in all your intermediate expressions and you'll make fewer errors of this sort.
Reply:You've got the right idea, but remember if you lose 100 joules of energy in one second (100 W), then across an entire day you will lose much more than this. So whatever your answer is at the end, it must be greater than 100 J.





With this in mind it's just a question of doing the maths (not always easy I know!). The only thing you did wrong here was that you divided by (60x60), instead of multiplying by it.





Therefore:





Energy lost per m^2 = 100 x 60 x 60 x 24 = 8640000 J/m^2 or 8.64 MJ/m^2





Scaling up for the total surface area = 8.64 MJ/m^2 x 1.8 m^2 = 15.6 MJ





(The prefix M stands for mega btw, and means 1 with 6 zeros after it).