1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Energy and Mass Problem

  1. May 6, 2007 #1
    1. The problem statement, all variables and given/known data
    The sun radiates energy at the rate of approximately 4 x 10^26 W. Assume that this energy is produced by a reaction whose net result is the fusion of 4 H nuclei to form 1 He nucleus, with the release of 25 MeV for each He nucleus formed.

    Calculate the sun's loss of mass per day

    2. Relevant equations

    E = mc^2

    3. The attempt at a solution

    I think all the information about the Helium reaction is a red herring, but I'm
    not sure. It's throwing me off. The problem says that the sun radiate energy
    at the rate of 4x10^26 W, but it doesn't say in what time frame.
    What I did at first, was assumed that that rate is per second and I did as follows;

    1 day = 24 hours = 24*60 minutes = 24*60*60 seconds = 86400 s

    Energy output in a day = 4x10^26 W/s * 86400s = 3.456 * 10^31 J

    then I used E = mc^2 -> m = E/c^2 = 3.456 * 10^31 J/(2.0 * 10^8 m/s)^2
    = 3.84 * 10^14 kg to be the amount of mass the sun loses every day.

    Is this right, or do I have to use the given information about the Helium reaction?
  2. jcsd
  3. May 6, 2007 #2
    I believe you are correct, its only asking for a mass equivalent of x amt of energy.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Energy Mass Problem Date
Energy,mass problem Aug 29, 2016
Rocket Equation-esque Problem Sep 17, 2015
Sam, Whose mass is 75kg . (Work Energy Problem) Dec 14, 2014
Re: conservation of energy problem(?) Oct 1, 2014