Angular revolution deceleration

[vorcil]

http://img15.imageshack.us/img15/858/masteringf.jpg

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:
$$\theta$$f=$$\theta$$i + $$\omega$$i * t + 1/2 $$\alpha$$ t^2

so i got the angle it turns through in radians being

wi * t + 1/2at^2

wi = 550*2$$\pi$$$$\underbrace{}_{}$$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$$\pi$$ = 30 revolutions

and i got it wrong





c: part three of the question:

wf = wi + at

0 = wf (from question) + at

wf = (150 *2$$\pi$$)/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

 

[vorcil]

anyone?

 

[Doc Al]

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.)

 

[vorcil]

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 $$omega$$i
i.e i used 400 rev/s^2 thanks for the help