Total acceleration from angular acceleration

[droidofthevoid]

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

 

[JeremyG]

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.

 

[droidofthevoid]

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?

 

[JeremyG]

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.

 

[droidofthevoid]

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

 

[JeremyG]

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?

 

[droidofthevoid]

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.

 

[JeremyG]

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