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Old Sep 10th 2010, 07:43 AM   #1
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General Principles

Represent each of the following combinations of units in the correct SI form using an appropriate prefix:
d) km*N

The answer in the back of the book was mm*N... Why?

Then the next question was to evaluate to three significant figures, and to express in SI using the appropriate prefix.

(200 kN)^2

Here's my work:
[200(10^3) N][200(10^3) N]
= 40 000(10^6) N^2
=40.0(10^9) N^2
=40.0 GN^2

the answer says 0.040MN^2
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Old Sep 10th 2010, 11:00 AM   #2
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For the first, I'm with you - the proper SI units are meters and newtons, not millimeters and newtons. For the second, remember that the power of 2 applies to both the M and N in MN. Hence 1 MN^2 = 10^6 x 10^6 N^2 = 10^12 N^2. Hence 4 x 10^10 N^2 = 0.04 MN^2. As another example of how this works, consider a square of size 1 KM^2. One square kilometer is not eqal to 1000 square meters, but rather is 1000m x 1000m = 10^6 m^2.
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