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Old Apr 14th 2011, 01:57 PM   #1
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Flywheel and tangential acceleration

A flywheel with a radius of 0.300 starts from rest and accelerates with a constant angular acceleration of 0.600
a) Compute the magnitude of the tangential acceleration, the radial acceleration, and the resultant acceleration of a point on its rim after it has turned through 60.0
I was able to compute a (tan) by:

(alpha)(r) = .6 (.300) = .18

a (rad) = v^2 / r = 0 / .300 = 0

a (total) = square root of a (cent)^2 + a (rad)^2 = .18

But for part "b", it is asking to solve for the same components after it has turned 60 degrees.

for a (tan), i used:

(.600)(.300) = .18

a (rad) = 0 + 2 (.600) (1.05) = 1.25
(i got the 1.05 from converting 60 degrees to radians)

for a (total) i ended up with 1.26 using:

square root of .18^2 + 1.25^2


I got the problem wrong. trying to figure out where i went wrong. Thanks in advance!
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Old Apr 15th 2011, 06:08 AM   #2
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Originally Posted by pre pt marc View Post
A flywheel with a radius of 0.300 starts from rest and accelerates with a constant angular acceleration of 0.600
a) Compute the magnitude of the tangential acceleration, the radial acceleration, and the resultant acceleration of a point on its rim after it has turned through 60.0
I was able to compute a (tan) by:

(alpha)(r) = .6 (.300) = .18

a (rad) = v^2 / r = 0 / .300 = 0

a (total) = square root of a (cent)^2 + a (rad)^2 = .18
Assuming that part a) is when the flywheel is at rest...(You never stated the question for part a) it seems.) Please use units on these. Otherwise, aside from writing the atot equation wrong (is it "a(cent)" or "a(tan)"?) this should be correct.

Originally Posted by pre pt marc View Post
But for part "b", it is asking to solve for the same components after it has turned 60 degrees.

for a (tan), i used:

(.600)(.300) = .18

a (rad) = 0 + 2 (.600) (1.05) = 1.25
(i got the 1.05 from converting 60 degrees to radians)

for a (total) i ended up with 1.26 using:

square root of .18^2 + 1.25^2
This is why you need to be more careful in writing your equations and use units. Take a look at the a(rad) equation. It looks like you are trying to compute a(rad) = (omega)^2 r. The trouble is you left out the r....

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Old Apr 15th 2011, 09:30 AM   #3
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Still a little confused. .

Thanks for the post, but i am afraid I am still a little confused as to how to finish solving this problem.

since a (cent) = (omega^2) (r), is it as simple as plugging in the 1.05 rad/s i computed by converting 60 degrees?

so a (cent) = (1.05 rad/s ^2) (.300m)

then, once i solve for a (cent), I simply plug in to:

a (total) = square root of a (cent)^2 + a (tan)^2?

I ended up coming up with:

a (cent) = .320

a (total) = .370

both of which were incorrect.
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Old Apr 15th 2011, 12:39 PM   #4
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Originally Posted by pre pt marc View Post
Thanks for the post, but i am afraid I am still a little confused as to how to finish solving this problem.

since a (cent) = (omega^2) (r), is it as simple as plugging in the 1.05 rad/s i computed by converting 60 degrees?

so a (cent) = (1.05 rad/s ^2) (.300m)

then, once i solve for a (cent), I simply plug in to:

a (total) = square root of a (cent)^2 + a (tan)^2?

I ended up coming up with:

a (cent) = .320

a (total) = .370


both of which were incorrect.
For a(cent), I'm getting
a(cent) = (omega)^2 * r = ( 2( alpha )*(theta) ) * r = ( 2(0.600)(pi/3) )*(0.300) = (1.2566)(0.300) = 0.37699 m/s^2

Perhaps you aren't keeping enough sig figs?

-Dan
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Last edited by topsquark; Apr 15th 2011 at 12:48 PM.
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