Kinetics of Rigid bodies

  • Thread starter Rob K
  • Start date
  • #1
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Homework Statement


The rotor of an electric motor of mass 200 kg has a radius of gyration of 150 mm. Calculate the torque required
to accelerate it from rest to 1,500 rev/min in 6 seconds. Friction resistance may be neglected.

Homework Equations


ƩMO = Iα
I = 1/2 (mr2
I am really really stuck here, I don't know what equations I need to use, if this were a straight line question I would use v = u + at, but it isn't so that is wrong


The Attempt at a Solution


All I have so far is this
I = 1/2 (mr2
I = 0.5 * 200 * 0.152
I = 2.25 kgm2

Really lost. I just need some pointers please.

Kind regards

Rob

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
PhanthomJay
Science Advisor
Homework Helper
Gold Member
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In calculating I, the radius of gyration is not the radius of a disk. You can look up the formula for it, which is [itex]r = \sqrt{I/m} [/itex] (and note how it is derived).

You can find the angular acceleration α using the kinematic equations of rotational motion (watch units).
 
  • #3
33
0
Brilliant, those are the words I didn't know to find the equation I couldn't find of variables I couldn't relate.

Found them all.

Thank you
 

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