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Angular revolution deceleration

  • Thread starter vorcil
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  • #1
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http://img15.imageshack.us/img15/858/masteringf.jpg [Broken]

a:
550-150 = 400rev change
400/60 = 6&2/3 rev/s (converted to revs)
6.66666 / 3.5 seconds = 1.9 rads^-2

since it's decelerating i put -1.9 rads^-2






now part two i got wrong,
b:
[tex]\theta[/tex]f=[tex]\theta[/tex]i + [tex]\omega[/tex]i * t + 1/2 [tex]\alpha[/tex] t^2

so i got the angle it turns through in radians being

wi * t + 1/2at^2

wi = 550*2[tex]\pi[/tex][tex]\underbrace{}_{}[/tex]t

wi = 57.59 rad/s (please check this i think this may be where i went wrong)


so radian angle = 57.59 *3.5 + (1/2*(-1.9) ) *3.5^2

i got 189 radians

189 / 2[tex]\pi[/tex] = 30 revolutions

and i got it wrong





c: part three of the question:

wf = wi + at

0 = wf (from question) + at

wf = (150 *2[tex]\pi[/tex])/60 = 15.7 rad/s

0 = 15.7 + (-1.9 *t)
-15.7/-1.9 = t
t=8.26 seconds

and i got it wrong
 
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Answers and Replies

  • #2
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anyone?
 
  • #3
Doc Al
Mentor
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a:
550-150 = 400rev change
400/60 = 6&2/3 rev/s (converted to revs)
6.66666 / 3.5 seconds = 1.9 rads^-2

since it's decelerating i put -1.9 rads^-2
This acceleration is in rev/sec^2, not rad/sec^2.

(This affects parts B and C.)
 
  • #4
393
0
This acceleration is in rev/sec^2, not rad/sec^2.

(This affects parts B and C.)
it was in rev/sec^2

i figured it out, i had used rev/min instead of rev/s with [tex]omega[/tex]i
i.e i used 400 rev/s^2 thanks for the help
 

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