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Only the best-physics(unit analysis) question

  1. Sep 2, 2007 #1
    Only the best--physics(unit analysis) question

    1. The problem statement, all variables and given/known data
    Ok, this is under the unit analysis section:

    -----------> We can express the radius of the fireball (resulting from a bomb) R in terms of t, ρ and E as R= const2x E^(1/x)t^(-y/x)ρ^(−z/x).
    Verify the relationship between R and t (That is R is proportional to t^(–y/x)) by plotting log (R) vs log (t) using the information provided in the pictures.
    Fit the data of log (R) vs log (t) with a straight line. What is the slope of the
    fit? What does the slope mean? Can you see why we are plotting log (R) vs
    log (t) instead of R vs t?

    --Basically, the pictures show the fireballs of a bomb with the diameter(m) at certain times(ms):

    2. Relevant equations
    - Is it me, or is the question too vague? I am trying to understand what it's asking and how I should answer.

    3. The attempt at a solution

    In the previous question, I have found z= 1 y= -2 and x= 5 for the values in the R=.... equation.

    However, I don't know what they mean by plotting the log and fitting the data. I have tried graphing log (x) and log (x^(2/5)) but it doens't seem correct.

    Thank you in advance.
    Last edited: Sep 2, 2007
  2. jcsd
  3. Sep 2, 2007 #2
    bump bump--help please!!!!!!
  4. Sep 2, 2007 #3
    please anyone???????
  5. Sep 2, 2007 #4


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    Staff Emeritus
    Science Advisor

    The times correct, particularly the second time.


    Normally when one has a function y = exp (kt), one can plot with semi-log, and the slope is the constant k.

    if one has R = A tn, then ln R = ln A + n ln t
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