# CAN ANYONE HELP ME WITH UNCERTAINTIES? Please :')

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I'm rather uncertain about them... hahaha.

No really, I'm unsure how to calculate them. Even on markschemes where I can see what the correct answer is, I have no idea how they got there!

For example, on the link below, on question 3(b) the markscheme gives an answer of 7.9 +- 1 / 1.5 / 2 N. But when I do it, I get 7.9 +- 0.5 N ! I don't understand!

Any help would be much appreciated, thanks :)

Posted: 03-01-11 09:04 by Gerald McBoingBoing

(uhm I hope this is not waaaay too late. Here is an answer anyhow.)

First off; what are you doing to get +-0.5N?

I have a feeling you have to calculate the standard deviation to get the uncertainty here... I'd go through it myself, but it's kind of late and I have a headache. If you do stats, it'll be a piece of cake...

If not, take the breaking force to be 'x' and the number of samples to be 'f'. Now, for each bar, find f times x^2. Add these all up to get the sum. Now, take away the mean squared. (seeing as you're getting the mean right, I'll take it that you're fine with that. Eheh.) Finally, square root your answer. With any luck, it's 1.5N; if not, uh, nevermind.

Also, I love your name. :D

Posted: 03-04-11 21:39 by Egg