Why is surface area included in Q=mcΔT for solar heating?

  • Thread starter Thread starter axer
  • Start date Start date
  • Tags Tags
    Area Energy Sun
Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
Sign up Log in
5 replies · 2K views
axer
Messages
35
Reaction score
4
Moved from a technical forum, so homework template missing
Hello, this isn't a homework or anything, I am just trying to understand one thing :) (finals are tomorrow :-0 )

If a person is exposed to heat energy of the sun for 4 hours(5040000 J per hour) and the avg surface area of the person is 1.9 m^2. and specific heat capacity of the body is 3470 J kg-1 k-1. mass of the person is 70. Calculate the rise of Temp.

Q=mc(delta T)

So here's what I am not understanding.. Should I include the person's area? but I am not seeing why they included that since the formula doesn't state area.

Answer in which area is included: (5040000*4)(1.9)=(70)(3470)T ... 158 C.
removing area from the answer: ... 83 C.
 

Discussion

Physics news on Phys.org
We can't answer your question because you didn't show any formula nor did you show your calculations.

Shouldn't 5040000 J per hour be J per m^2 per hour?
 
anorlunda said:
We can't answer your question because you didn't show any formula nor did you show your calculations.

Shouldn't 5040000 J per hour be J per m^2 per hour?
Ok sorry if I am not clear
Power=Energy/time= 5040000 j/h=5040000 W

Heat energy from the sun in 4 hours= 20160000 J. my question is should we include the area to find the heat energy? if yes, why? thanks.
 
axer said:
Ok sorry if I am not clear
Power=Energy/time= 5040000 j/h=5040000 W

Heat energy from the sun in 4 hours= 20160000 J. my question is should we include the area to find the heat energy? if yes, why? thanks.

Nope, you're still far off in magnitude and units. Is the 20160000 supposed to be for the entire Earth? That doesn't work either.

Also, a watt is one joule per second, not one joule per hour.
.
https://en.wikipedia.org/wiki/Sunlight said:
The World Meteorological Organization uses the term "sunshine duration" to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter.
 
anorlunda said:
Nope, you're still far off in magnitude and units. Is the 20160000 supposed to be for the entire Earth? That doesn't work either.

Also, a watt is one joule per second, not one joule per hour.
.
nA3LyMzoSdWzskYPvQBy4Q.png
So here's the 2 part question, sorry if my way of phrasing is unclear.
 

Attachments

  • nA3LyMzoSdWzskYPvQBy4Q.png
    nA3LyMzoSdWzskYPvQBy4Q.png
    31.1 KB · Views: 296
axer said:
[image contents converted to text]
(ii) One square metre of the Earth's surface receives approximately 1.4 x 103 J of solar energy per second
The highlighted portion of the question is important.