course phy 121 ҽޠ䬈ݧ~xassignment #003
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18:18:46 Query Principles of Physics and General College Physics: Summarize your solution to Problem 1.19 (1.80 m + 142.5 cm + 5.34 `micro m to appropriate # of significant figures)
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RESPONSE --> I converted all of the numbers to meters and added them together. 1.80m + 1.425m + .534m = 3.759m Because the numbers all have three significant figures I need to make my answer have three therefore I rounded it to 3.76m confidence assessment: 2
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18:29:53 ** 1.80 m has three significant figures (leading zeros don't count, neither to trailing zeros unless there is a decimal point; however zeros which are listed after the decimal point are significant; that's the only way we have of distinguishing, say, 1.80 meter (read to the nearest .01 m, i.e., nearest cm) and 1.000 meter (read to the nearest millimeter). Therefore nothing smaller than .01 m can be distinguished. 142.5 cm is 1.425 m, good to within .001 m. 5.34 * `micro m means 5.34 * 10^-6 m, or .00000534 m, accurate to within .00000001 m. When these are added you get 3.22500534 m; however the 1.80 m is not resolved beyond .01 m so the result is 3.23 m. Remaining figures are meaningless, since the 1.80 m itself could be off by as much as .01 m. **
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RESPONSE --> The answer in the back of the book is 3.76m not 3.23m. I did make the mistake of saying that they all had three significant figures when they didn't. However I did the following differently than you and came up with the answer in the back of the book. The final number in the equation was 5.34 x 10^5 micro meter. So first I converted the scientific notation 5.34 x 10^5 portion to 534000 micro meters then I converted micro meters to meters by using the 10^-6 so I moved the decimal over making the number .534m This added to 1.80m and 1.425m = 3.759m. The smallest number of significant figures in the equation is 3 so I rounded it to 3.76m self critique assessment: 2
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18:30:09 University Physics #34: Summarize your solution to Problem 1.34 (4 km on line then 3.1 km after 45 deg turn by components, verify by scaled sketch).
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RESPONSE --> not applicable confidence assessment: 3
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18:30:21 ** THE FOLLOWING CORRECT SOLUTION WAS GIVEN BY A STUDENT: The components of vectors A (2.6km in the y direction) and B (4.0km in the x direction) are known. We find the components of vector C(of length 3.1km) by using the sin and cos functions. }Cx was 3.1 km * cos(45 deg) = 2.19. Adding the x component of the second vector, 4.0, we get 6.19km. Cy was 2.19 and i added the 2.6 km y displacement of the first vector to get 4.79. So Rx = 6.19 km and Ry = 4.79 km. To get vector R, i used the pythagorean theorem to get the magnitude of vector R, which was sqrt( (6.29 km)^2 + (4.79 km)^2 ) = 7.3 km. The angle is theta = arctan(Ry / Rx) = arctan(4.79 / 6.19) = 37.7 degrees. **
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RESPONSE --> self critique assessment: 3
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