Total acceleration from angular acceleration

  • #1

Homework Statement


A discus thrower ( with arm length of 1.2 m) starts from rest and begins to rotate counterclockwise with a constant angular acceleration of 2.5 [rad/s^2]. What is the magnitude of the total acceleration of the discus when its angular velocity is 9.0[rad/s]?

Homework Equations


I'm not really connecting the dots here. Do I treat the discus thrower as a rigid body and give a simple moment of inertia, which I then plug into a torque equation tau = I alpha?



The Attempt at a Solution

 

Answers and Replies

  • #2
62
16
Do I treat the discus thrower as a rigid body
Not necessary. The question is interested in the acceleration of the discus, so there is only a need to consider the motion of the discus.
 
  • #3
Not necessary. The question is interested in the acceleration of the discus, so there is only a need to consider the motion of the discus.
So then I treat it as a particle going in a circle and use a = R alpha? Do I neglect the omega= 3.0 rad/s?
 
  • #4
62
16
o then I treat it as a particle going in a circle and use a = R alpha?
Yes in this case you can treat it as a particle going round in a circle. ##a = r\alpha## will give you what kind of acceleration? As a hint, see the comment below as well.

omega= 3.0 rad/s?
You mean 9rad/s? No you do not ignore this.
 
  • #5
Yes in this case you can treat it as a particle going round in a circle. ##a = r\alpha## will give you what kind of acceleration? As a hint, see the comment below as well.



It'll give tangential acceleration
 
  • #6
62
16
Yes, the question wants the total acceleration, so that should give you a clue that it is not just tangential acceleration at play here. What else?
 
  • #7
Yes, the question wants the total acceleration, so that should give you a clue that it is not just tangential acceleration at play here. What else?
Well then, I would presume it would have something to do with torque and perhaps treating the thrower as a rigid body? or radial acceleration, which would be omega squared times r.
 
  • #8
62
16
Torque by the thrower is the cause for the tangential acceleration/angular acceleration of the discus. And as mentioned above, the thrower himself need not be considered in this problem.

The discus is travelling in a circular motion, yes? Tangential acceleration is not sufficient to ensure that the discus is travelling in a circular motion, uniform or not. What about considering the radial acceleration?
 

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