A levels Physics - Significant Figures & Uncertainty

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richie.harvy
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I calculated a value for g
(9.63 ms-2) in a question. I’ve given the answer in 3sf since the values in the question are in 3sf.

Then I’m supposed to calculate the % uncertainty(I’m given the % uncertainty for individual values so I’m just supposed to add them up). The uncertainty is 8%.

I’m then supposed to calculate the absolute uncertainty. And this is where the issue is. The marking scheme says:
0.08 * 9.6 (NOT 9.63) = 0.8 (1d.p)
Whereas, I would do:
0.08 * 9.63 = 0.77 (2 d.p to match with the value).

Why is my answer incorrect??
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richie.harvy
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The question^
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richie.harvy
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(Original post by richie.harvy)
I calculated a value for g
(9.63 ms-2) in a question. I’ve given the answer in 3sf since the values in the question are in 3sf.

Then I’m supposed to calculate the % uncertainty(I’m given the % uncertainty for individual values so I’m just supposed to add them up). The uncertainty is 8%.

I’m then supposed to calculate the absolute uncertainty. And this is where the issue is. The marking scheme says:
0.08 * 9.6 (NOT 9.63) = 0.8 (1d.p)
Whereas, I would do:
0.08 * 9.63 = 0.77 (2 d.p to match with the value).

Why is my answer incorrect??
Also, generally, what are the rules when it comes to sig. figs/ decimal places of uncertainties (both % and absolute) and the corresponding value? It’s a BIG grey area for me!
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