Understanding process

1. Apr 25, 2013

MMCS

attached is an example question i am working through, i would appreciate if anybody could explain to me the part in the red box.

I understand the relationship

however, this working appears to divide the angular equation by the radius???

thanks

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2. Apr 25, 2013

milesyoung

The equation just above it:
P*r = Tf + I*α

Do you understand that one?

3. Apr 25, 2013

MMCS

oh yes, of course, i assumed it was a subscript not a multiplication of radius (where the tansion force would be acting) been looking at it too long i think, thanks for your help milesyoung

4. Apr 25, 2013

milesyoung

No problem, whoever wrote the solution should have stuck to Rd.

Edit:
Also, if something seems off about the equation you're working with, try comparing the units of whatever quantity you have on the LHS and RHS. Something might be rotten in the state of Denmark.

Last edited: Apr 25, 2013