# Circular motion

An exhaust fan rotates at 9.0 x 10^2 revolutions per minute. Find the acceleration of a point on a blade at a distance of 25cm from the axis of rotation.

I don't know where to begin. Can someone help?

## Answers and Replies

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dextercioby
Science Advisor
Homework Helper
How about:what theory would have to use to get it solved...?Formulas and a reasoning for using them...

Open your book.

Daniel.

Ok I think the ? has to do with uniform circular motion. The only equation I am given is a (sub) c = v^2 divided by r
A (sub) c = centripetal acceleration
v = velocity
r = radius

dextercioby
Science Advisor
Homework Helper
$a_{cp}=\omega^{2} r$ is the formula that u need.

U have been give the frequency.Find the angular velocity "omega"...

Daniel.

isnt that the same formula i just gave you?

dextercioby
Science Advisor
Homework Helper
Not really.There's a close connection between the 2,though.So do it.

Daniel.

that is the problem I don't know how

dextercioby
Science Advisor
Homework Helper
$$a_{cp}=(2\pi\nu)^{2}r$$

U know "r" and u know "nu",now find the acceleration.Convert from revs/min to Hz...

Daniel.

the question has nothing to do with frequency

dextercioby
Science Advisor
Homework Helper
If you don't see it,that's bad.

"rotates at 9.0 x 10^2 revolutions per minute"...what does that mean?

Daniel.

the answer i am supposed to get has nothing to do with frequency. all i need to know is the acceleration. no where in our notes and in our class did we talk about frequency.

dextercioby
Science Advisor
Homework Helper
Incidentally,in this problem you are given the frequency & the distance between the point & the center of the circle.

I can't do anything more.I've already told u what to do...

Daniel.

Johnf2004,
In the given quetion you are given the frequency,f i.e. number of revolutions per minute. You can convert this into time period, T using:
T = 2*pi/f

Now use $$v = \frac{2 \pi r}{T}$$
as for an object moving with constant speed on a circular path, v = s/t
Here, the distance,s is the circumference(2*pi*r) traversed in time t. But then t, the time is also equal to time taken for one complete revolution, hence equal to T.

acceleration = (v^2)/r

What dextercioby has explained is same , he started with $$\omega$$, the angular velocity

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