Physics Help Forum General Principles

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Sep 10th 2010, 07:43 AM #1 Junior Member   Join Date: Sep 2010 Posts: 24 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
 Sep 10th 2010, 11:00 AM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,339 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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