1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Avg. temperature rise & energy conversion

  1. Nov 28, 2007 #1
    The problem is: The sun is 1.5x10^11 meters from the earth. Energy from the sun is received at the earth's surface at the rate of 1.4 kilowatts per square meter. I'm trying to find two answers:
    1. This energy flux from the Sun falls on a pond of water 100 square meters in area and 0.1 meter in depth. Assume all of this energy heats the water. Find the average temp. rise of the pond after 10^3 seconds
    2. Determine the rate in kilograms per second at which the sun's mass is being converted to energy.

    For 1, energy flux is Iota=power/area, power=work/time,
    For 2, the SA of a sphere is 4pir^2, E=mc^2

    So far I have p/1000 for energy flux and power=w/1000. I'm stuck on what to do next, but since the question gives you the distance between the earth and sun, would w=fd help you find the solution? This question seems unusual compared to ones I've done in the past.
  2. jcsd
  3. Dec 1, 2007 #2
    definition of a kilowatt

    Remember that a kilowatt is 1000 watts, which is 1000 joules/second.

    Hence, the flux is (1400 joules/second)/100 meters squared, which is 140 joules per meter squared second.

    I am not so sure about the rest of the problem, but perhaps this information will help you. I will keep looking at it, though.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook