A rim unwinding from a string due to gravity.

  • Thread starter Eats Dirt
  • Start date
  • #1
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Homework Statement




A string is wrapped around a small hoop several times. the radius is 8cm and mass 0.18 kg. the string is released from rest after the hoop has descended 75 cm what is the angular speed of the rotating hoop and the speed at its centre?

Homework Equations




mgh 1/2 Iw^2

The Attempt at a Solution



MGH energy is conserved so mgh=1/2Iw^2
i sub in and solve except this does'nt give the right answer.
 

Answers and Replies

  • #2
998
15
If I is the moment of inertia of hoop about its centre then,
intial energy = final energy
GPE = KE of translation + KE of rotation
 
  • #3
998
15
mgh = (1/2)mv[itex]^{2}[/itex] + (1/2)I[itex]\omega[/itex][itex]^{2}[/itex]
 

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