moe6142 Posts: 11, Reputation: 1 New Member #1 Nov 9, 2008, 11:49 AM
significant digit
88.375/1264.7=

234.6+89x6.8=

471-22.85=

calculate all questions to the correct significant digit
 Credendovidis Posts: 1,593, Reputation: 66 - #2 Nov 9, 2008, 06:40 PM

Have you done the 3 calculations already?
If so : what have did you get so far?
You do not seriously expect us to do your homework, don't you?

:)
 Credendovidis Posts: 1,593, Reputation: 66 - #3 Nov 11, 2008, 05:36 PM
Originally Posted by moe6142
you ar enot telling me the answer
Of course I don't. It is not my homework, it is your homework.
I just provided you with some guidelines on how to get to the proper answer.

I suggested :

Have you done the 3 calculations already? - You did not answer : I doubt you did any calculations.
If so : what have did you get so far? - Lacking answers and calculations how to know what you missed ?
You do not seriously expect us to do your homework, don't you? - Apparently you did ...

:rolleyes:
 lovebug2140 Posts: 49, Reputation: -1 Junior Member #4 Nov 12, 2008, 12:04 AM
Comment on Credendovidis's post
Just balancing for you :)
 moe6142 Posts: 11, Reputation: 1 New Member #5 Nov 12, 2008, 06:55 AM
Originally Posted by Credendovidis
Of course I don't. It is not my homework, it is your homework.
I just provided you with some guidelines on how to get to the proper answer.

I suggested :

Have you done the 3 calculations already? - You did not answer : I doubt you did any calculations.
If so : what have did you get so far? - Lacking answers and calculations how to know what you missed ?
You do not seriously expect us to do your homework, don't you? - Apparently you did ...

:rolleyes:

88.375/1264.7=0.069878

234.6+89x6.8=840

471-22.85=448
 ebaines Posts: 12,129, Reputation: 1307 Expert #6 Nov 12, 2008, 08:30 AM

I think you are including too many digits in some of your answers . For example:

234.6 + 89*6.8 has only 2 significant digits. But your answer (840) has 3. I would rewrite using scientific notation, like this:

8.4 x 10^2

This way it's clear that there are only 2 significant digits ( 8 and 4)
 Credendovidis Posts: 1,593, Reputation: 66 - #7 Nov 12, 2008, 06:01 PM
moe6142

calculate all questions to the correct significant digit

a = 88.375/1264.7=0.069878 --> = 6.98788...

b = 234.6+89x6.8=840 --------> = 839.8 (not 840)

c = 471-22.85=448 -----------> = 448.15

I have to assume that in your lesbook the meaning of "correct significant digit" has been explained.
So now the question : what does that "correct significant digit" mean here?
And what is that than in each of these three replies ?

(I can not sit next to you during your next exam, so that is why YOU have to do your homework yourself... )

:)

.

.
 Unknown008 Posts: 8,076, Reputation: 723 Uber Member #8 Nov 13, 2008, 01:49 AM

Hmmm... I may be wrong, but I think that the number of significant figures you need to give is already given in the question itself.

88.375/1264.7= (all are 5 sig fig; answer in 5 sig fig)

234.6+89x6.8= (highest sig fig = 4; answer in 4 sig fig)

471-22.85= (highest sig fig = 4; answer in 4 sig fig)
 Capuchin Posts: 5,255, Reputation: 656 Uber Member #9 Nov 13, 2008, 01:53 AM

In a physics setting, you want to use the lowest sig fig, as this is the lowest accuracy of all your measurements.

But the question is silly, as these seem to be pure maths questions where there's no justification for quoting to a certain sig fig.
 Unknown008 Posts: 8,076, Reputation: 723 Uber Member #10 Nov 13, 2008, 02:14 AM

I'm not so following well here... You said:

"In a physics setting, you want to use the lowest sig fig"

Lowest? I thought that physics was a subject of accuracy?? Of course that one should not try to get into too much accuracy, for fear that the result is wrong... but still!
 Capuchin Posts: 5,255, Reputation: 656 Uber Member #11 Nov 13, 2008, 05:25 AM
Originally Posted by Unknown008
I'm not so following well here... You said:

"In a physics setting, you want to use the lowest sig fig"

Lowest? I thought that physics was a subject of accuracy??? Of course that one should not try to get into too much accuracy, for fear that the result is wrong... but still!
Well, for example, if you measure the radius of a circle as 4.1m with a ruler. You also measure the speed of an object moving along the circle as 5.2m/s using a meter wheel and a stopwatch. Now, you also measure the mass of the object with a highly accurate, calibrated scale, and this gives you a mass of 3.456789kg.

Now in working out the centripetal force $F=\frac{mv^2}{r}$ we put in the numbers and get an answer as 22.797945N

However, are we justified in quoting it to that many significant figures? No, because our speed and radius measurements were only accurate to 2 sig figs, so this means that our answer can only really be meaningful to 2 sig figs. So a better answer would be to say the force is 23N, because that lets other people know when they read your work, that you're accurate to 2 sig figs. All the effort that you put into measuring the mass accurately is meaningless because you're multiplying it by innaccurate measurements which have a higher error associated with it. If you quoted your answer as 22.797945N, you would be giving the false impression that your measurements were more accurate than they were.

For instance you speed would be +/- 0.05 m/s ans your radius would be +/- 0.05, but your mass measurement is +/- 0.0000005, but this is completely negligible compared to the error in your other measurements, so you have to let them take precident.

I think you have the wrong idea upon reading what you wrote Jerry. By quoting to only 2 sig figs in this case, you are being more accurate. You are just being less precise - which is fine if some of your measurements aren't precise (they're still accurate! ).

You should look up the difference between precision and accuracy. Accuracy is important - precision is less important but nice if you can get it.
 Unknown008 Posts: 8,076, Reputation: 723 Uber Member #12 Nov 19, 2008, 02:30 AM

Oh, OK! I get it better. Thanks Cap! :)
 colbtech Posts: 740, Reputation: 65 Senior Member #13 Nov 19, 2008, 02:33 AM

7 for my 10p worth!

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