Angular motion homework problem

AI Thread Summary
The discussion revolves around a physics homework problem involving an electric motor's grinding wheel that stops due to constant negative angular acceleration. The user successfully calculated the time it takes for the wheel to stop, which is 3.77 seconds. However, they initially struggled with calculating the angular displacement in radians, resulting in an incorrect negative value. The issue was identified as an extra negative sign in their calculations. The user ultimately resolved the confusion and sought further assistance.
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Homework Statement



An electric motor rotating a workshop grinding wheel at a rate of 90 rev/min is switched off. Assume constant negative angular acceleration of magnitude 2.50 rad/s2.
(a) How long does it take for the grinding wheel to stop?

(b) Through how many radians has the wheel turned during the interval found in (a)?

Homework Equations


wf=wi+at^s
theta= 1/2 (wi+wf)t

The Attempt at a Solution


I got the right answer for (a) which was 3.77 sec so for (b) I thought that all you needed to do was plug in the values into the second equation to get theta but the answer I got was wrong. I got -17.766...I don't know what I'm doing wrong...any help would be appreciated.
 
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uuh lol never mind i just had an extra negative sign
 

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
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Thread 'A cylinder connected to a hanging mass'

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