Steady state behavior for a particle undergoing damped forced oscillations

  • Thread starter elsamp123
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  • #1
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Homework Statement


consider a system with a damping force undergoing forced oscillations at an angular frequency ω
a) what is the instantaneous kinetic energy of the system?
b) what is the instantaneous potential energy of the system?
c) what is the ratio of the average kinetic energy to the average potential energy? express the answer in terms of the ratio ω/ω0
d) for what values of ω are the average kinetic energy and the average potential energy equal? what is the total energy of the system under these conditions?
e) how does the total energy of the system vary with time for an arbitrary value of ω? for what values of ω is the total energy constant in time?


Homework Equations


x = A cos(ωt-δ)
A(ω) = (F0 /mω02) [(ω0/ω)/[(ω0/ω-ω/ω0)2+(1/Q2)]1/2)]

The Attempt at a Solution


i know that K.E = 1/2 m (dx/dt)2

and P.E = 1/2 kx2

so part and b ive got .. but how do u go about calculating the Avg K.E?
 

Answers and Replies

  • #2
vela
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You want to integrate the kinetic energy over one cycle:
[tex]\langle K \rangle = \frac{1}{T}\int_0^T \frac{1}{2}mv(t)^2\,dt[/tex]where T is the period of oscillation.
 
  • #3
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So I would go:

ω/2∏ [itex]\int^{ω/(2∏)}_{0}[/itex] 1/2 m (dx/dt)2?

so would P.E go from 0 to A then?

Thanks a ton btw! you really helped me get started with this HW
 
  • #4
vela
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You'd still average the potential over one cycle by integrating with respect to time and dividing by the period.
 
  • #5
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Thank you so very much! You are very kind! :)
 

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