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Homework Help: Equations of motion and proper Significant Digits.

  1. Sep 24, 2007 #1
    1. The problem statement, all variables and given/known data

    Solve the following to the proper number of significant figures:

    a) A loaded truck has mass (2.12 X 10^4 +/- 6 X 10^2) kg and when empty, it has a mass of (1.72 X 10^4 +/- 5 X 10^2) kg. What is the relative uncertainty of the mass of the gravel dumped from the truck?

    3. The attempt at a solution

    Ok, so I go through the math and get

    Relative Uncertainty = (5 X 10^2 + 6 X 10^2) kg / 4000 = 0.275

    My qwuestion is in regards to significant digits. According to me, the # of sig. figs. Here is 1……there is 1 sig. fig. in 5 X 10^2 or 6 X 10^2, whichever you look at, so the answer should be rounded off to one significant figure.

    This means that the FINAL answer should be 0.3.

    b) v(initial) = 10.5 m/s
    v(final) = -7.3 m/s
    t = 0.0115 s

    Calculate a.

    3. The attempt at a solution

    I used v(final ) = v(initial) + at and got a = 1533 m/s^2.

    Should the correct answer (rounded off to proper number of significant figures) be a = 1.53 X 10^3 m/s^2?

    What about 1533 m/s^2 or 1530 m/s^2….would either of these be acceptable OR is the only answer 1.53 X 10^3 m/s^2?
  2. jcsd
  3. Sep 25, 2007 #2
    Your help would be greatly appreciated. I feel like I am close but just need some help finishing off the problems.
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