1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Total acceleration from angular acceleration

  1. Dec 13, 2015 #1
    1. The problem statement, all variables and given/known data
    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]?

    2. Relevant 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?

    3. The attempt at a solution
  2. jcsd
  3. Dec 13, 2015 #2
    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.
  4. Dec 13, 2015 #3
    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?
  5. Dec 13, 2015 #4
    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.

    You mean 9rad/s? No you do not ignore this.
  6. Dec 13, 2015 #5
  7. Dec 13, 2015 #6
    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?
  8. Dec 13, 2015 #7
    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.
  9. Dec 13, 2015 #8
    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?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted