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: Heat Problems

  1. Oct 20, 2005 #1
    I am unsure about some of my formulae and answers I would be very grateful if someone could clarify these please

    Q1 The insulating layer on the inner wall of a building is made from a
    compound layer of laminated board (inner) and styrofoam (outer). The
    thickness of the board is 0.02 m and of the styrofoam, 0.06 m. If the
    temperature at the surfaces of the layer are 20C (inner) and 5C (outer),
    calculate the rate of flow of heat per m 2 through the layer and the
    temperature at the board-styrofoam interface. The thermal conductivities
    are 0.1 Js -1 m -1 C -1 for the board and 0.01 J s -1 m -1 C -1 for the styrofoam.

    used the formula R=L/k to find the resistance of both then subbed in formula P=A(T2-T1)/(R1+R2)
    Answer 2.42W

    Q2 Calculate the surface temperature of a human body of surface area 1.2
    m 2 , which emits radiation at a rate of 597 W. Assume that the body
    behaves as a perfect black body. If the temperature of the surroundings is
    18° °° °C, calculate the net loss of heat by radiation by the body.

    Used the formula Aε(5.6703x10^-8)T^4=Q/T=P

    Answer T=306.10k
    Orig temp T=291.16k
    Answer 108.31W

    Q3 Calculate the root mean square speed of nitrogen
    molecules at 20 C. At what temperatures will the RMS speed be a) half that
    value and b) twice that value?
    The molar mass of nitrogen is 28x10 -3 kg mol -1 .

    Vrms=sq root 3RT/M
    Answer 510.89
    Answer 2 73.28k
    Answer 3 1,172.60k

    Please confirm if these are done correctly or if not please lead me in the right direction thanks!
  2. jcsd
  3. Oct 20, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook