Rotational KINEMATICS (confusing)

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Homework Help Overview

The discussion revolves around a problem in rotational kinematics involving a toy train that accelerates while moving along a circular track. Participants are exploring the calculation of angular acceleration based on given linear speeds and the radius of the track.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to calculate angular acceleration using kinematic equations for rotational motion, but expresses confusion regarding their reasoning and the correctness of their calculations. Other participants question the relationship between angular and tangential speeds, and some suggest alternative methods for finding angular velocities.

Discussion Status

Participants are actively engaging with the problem, offering insights into the relationships between linear and angular quantities. There is a mix of interpretations regarding the calculations and methods, with some guidance provided on how to approach finding angular velocities and their connection to linear speeds.

Contextual Notes

There are indications of confusion regarding the steps involved in the calculations, particularly in relating angular and tangential speeds. The original poster's calculations have not been confirmed as correct, and there is a lack of consensus on the best approach to take.

avenkat0
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Homework Statement


a) A 1.79 kg toy train accelerates constantly from 0.82 m/s to 3.43 m/s in 0.479 revolutions while traveling around a circular track of r 16.7 cm. Find:

- α, magnitude of the angular acceleration.

Homework Equations


img23.gif

img22.gif

The Attempt at a Solution


  1. I first tried getting θ=(.479)(2pi)=3.009
  2. Then I found both the ωf and the ωo by finding the frequencies... I did this by first finding the distence covered by the partial revolution then using the velocity. I did this for both the ω's...
  3. Then i simply used the kinematic analog equation for rotational bodies and got α to be .00656 rad/sec2 and this came out to be wrong
Is there a flaw in my reasoning
Thank You
 

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avenkat0 said:
Then I found both the ωf and the ωo by finding the frequencies... I did this by first finding the distence covered by the partial revolution then using the velocity. I did this for both the ω's...
I don't quite understand this step. Angular and tangential speeds are related by v = ωr.
 
Isn't w-2pi(f)
 
avenkat0 said:
Isn't w-2pi(f)
Do you mean does ω = 2pi(f)? Sure, you could think of it that way, but I don't see the point. You are given the linear speeds and the radius, so the angular speeds can be found immediately. (But, done correctly, you should get the same answer either way. Does your method give you the same answer?)
 
Ooh so after I find the angular velocity I would just Use the equations to find alpha??

And can you also explain why the tangental and angular velocities are related by v=omega (r)... Will an object traveling at 5 m/s linearly be going at 2.5 rad/s because it's going around a circle with radius 2?
 
Last edited:
avenkat0 said:
Ooh so after I find the angular velocity I would just Use the equations to find alpha??
Sure.
And can you also explain why the tangental and angular velocities are related by v=omega (r)... Will an object traveling at 5 m/s linearly be going at 2.5 rad/s because it's going around a circle with radius 2?
Yes.

Read this: Rotational Quantities
 

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