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# Three Physics questions (struggling =S) watch

1. 1) You measure the thinkness of a sheet of paper to be 0.2 +- (plus minus) 0.04mm. Show that the percentage uncertainty is +- 20%.

2) You measure the thickness of square cross section of rubber cord using a ruler. You get the result 5.0 +- 0.5mm. Show that the percentage uncertainty in the cross-sectional area is +- 20%.

3) In measuring the Young modulus of copper wire you obtain values: length of wire = 1.5 +- 0.005m; diameter of wire = 0.00 +-0.02mm; extension = 3.5 +-0.02mm; tensile force = 11.5+-0.5N. Show that the largest percentage uncertainty is +-6%. Explain why this uncertainty is particularly importand in this case.

Thank you
2. 1) well you have the thickness which is 0.2 (cm?), and there can be an error of + or - 0.04... simply find what percentage 0.04 is in 0.2....

2) same as above, but it's a square, and because you are finding the area you are effectively multiplying uncertanties, when you multiply, you add percentage errors together...

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