Inertia Question: Resolve the Wheel Motion

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The discussion revolves around calculating the angular acceleration, angular speed, revolutions per second, and kinetic energy of a metal wheel with a specified radius, mass, and torque. Participants express confusion over the kinetic energy calculation, initially yielding results in millijoules instead of joules, leading to questions about the validity of the small energy value. There is a consensus that the torque operates over one minute, which is not the period of rotation, affecting the calculations. Clarifications are requested regarding the numerical work and the formulas used, as some participants find the results questionable. The thread emphasizes the importance of detailed calculations to resolve discrepancies in energy values.
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Homework Statement



The full metal wheel of radius 30 cm, 300 kg of mass moment of inertia I = 1/2 (mr ^ 2) operating torque 50nm in time 1 min. Determine the angular acceleration, angular speed of wheel, revolutions per second, revolutions that the wheel makes to achieve this speed, kinetic energy.

Homework Equations



ω = 2∏/T, s=1/2(αt^2), Ek=(Iω^2)/2, I = 1/2 (mr ^ 2)

The Attempt at a Solution



First I can get ω, T=60sec, so ω=∏/30...

So I can get all of this using those few formulas, but in the end I get kinetic energy in mJ??
 
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the_man said:

Homework Statement



The full metal wheel of radius 30 cm, 300 kg of mass moment of inertia I = 1/2 (mr ^ 2) operating torque 50nm in time 1 min. Determine the angular acceleration, angular speed of wheel, revolutions per second, revolutions that the wheel makes to achieve this speed, kinetic energy.

Homework Equations



ω = 2∏/T, s=1/2(αt^2), Ek=(Iω^2)/2, I = 1/2 (mr ^ 2)

The Attempt at a Solution



First I can get ω, T=60sec, so ω=∏/30...

So I can get all of this using those few formulas, but in the end I get kinetic energy in mJ??
Why not get kinetic energy in Joules ?
 
SammyS said:
Why not get kinetic energy in Joules ?

I can get energy in Jules but then its very small number, but i don't get it why is a small number?
 
the_man said:

Homework Statement



The full metal wheel of radius 30 cm, 300 kg of mass moment of inertia I = 1/2 (mr ^ 2) operating torque 50nm in time 1 min. Determine the angular acceleration, angular speed of wheel, revolutions per second, revolutions that the wheel makes to achieve this speed, kinetic energy.

Homework Equations



ω = 2∏/T, s=1/2(αt^2), Ek=(Iω^2)/2, I = 1/2 (mr ^ 2)

The Attempt at a Solution



First I can get ω, T=60sec, so ω=∏/30...

So I can get all of this using those few formulas, but in the end I get kinetic energy in mJ??

The torque is acting for 1 minute; The given time of 1 minute is not the period of oscillation or rotation...
 
Okay. I got it! Now its Ek=7,5kJ
 
Perhaps you should elaborate on your calculations; To me, 7.5 kJ doesn't look right.
 
gneill said:
Perhaps you should elaborate on your calculations; To me, 7.5 kJ doesn't look right.

M=F*r
F=m*α
α=ω/T
Ek=(Iω^2)/2
 
the_man said:
M=F*r
F=m*α
α=ω/T
Ek=(Iω^2)/2

I see a collection of formulas, at least one of which is rather dubious, but no calculations. Can you show your numerical work and explain what the steps are that your taking?
 
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