Angular Acceleration of a Moving Wheel

[underoathP]

I am having a bit of trouble with the following problem.

A cyclist starts from rest and pedals so that the wheels make 8.5 revolutions in the first 4.6 s. What is the angular acceleration of the wheels (assumed constant)?

I multiplied 8.5 by 2pi and then divided by 4.6 sec. I get an answer of 11.6 rad/sec, but they want an answer in rad/sec^2. Am I doing this right?

 

[Hootenanny]

I am having a bit of trouble with the following problem.

A cyclist starts from rest and pedals so that the wheels make 8.5 revolutions in the first 4.6 s. What is the angular acceleration of the wheels (assumed constant)?

I multiplied 8.5 by 2pi and then divided by 4.6 sec. I get an answer of 11.6 rad/sec, but they want an answer in rad/sec^2. Am I doing this right?

I see you've found the Homework Forums, .

Not quite. What is the definition of angular acceleration?

 

[underoathP]

Angular Acceleration

The definition of angular acceleration is angular velocity over time. So, to get angular velocity from 8.5 rev/4.6 sec you have to find the angular velocity first. So, the definition of angular velocity (omega) is angular displacement over time, and the angular displacement is in radians. That is why I multiplied 8.5 by 2pi. Do I have to divide by 4.6 again?

 

[Hootenanny]

Try having a look at this page; http://hyperphysics.phy-astr.gsu.edu/hbase/rotq.html#drot and in particular, the Description of Rotation section paying close attention to the kinematic equations...

 

[underoathP]

I looked at that website and this is what makes sense to me:

8.5 rev * 2pi = 53.41 radians
53.41 rad / 4.6 sec = 11.61 rad/sec (omega)
11.61 rad/sec / sec = 2.5 rad/sec^2

2.5 is the wrong answer when I entered it. I am out of ideas.

 

[Hootenanny]

I looked at that website and this is what makes sense to me:

8.5 rev * 2pi = 53.41 radians
53.41 rad / 4.6 sec = 11.61 rad/sec (omega)
11.61 rad/sec / sec = 2.5 rad/sec^2

2.5 is the wrong answer when I entered it. I am out of ideas.

Okay, how about this section of the website;

Which equation do you suppose would be appropriate in this case?

 

[shaanyr]

wait what happened to this? was there an answer discussed? I am so confused! i have a very similar problem and I am doing the same thing.

I think the right equation is w^2= wi^2+2a(theta)

but i used that assuming the initial angular velocity is 0 and its wrong