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impendingChaos
Apr18-07, 07:38 PM
1. The problem statement, all variables and given/known data
Need to energy dissipation by the drap force on a ball in free fall from height h and when it has reached terminal speed, assuming it happens before it hits thr ground. Drag force has magnitude bv^2, where b is drag coefficient and v is instantaneous speed of the ball.


2. Relevant equations

I have calculated in an earlier part of the problem that terminal velocity:
Vt=root(mg/b)

Also, isnt the energy dissipation equation:
Ediss=mgh

3. The attempt at a solution

I have the above equations but am unclear where to move next.

denverdoc
Apr18-07, 08:04 PM
Not sure what you mean by Ediss=mgh. If chosing conservation of energy, one could simply assume that the drag energy(work) is the difference between the final and initial sums of PE and KE. The problem I see, is that the eqn you posted for Vt says nothing about height.

In other words if we knew the distance required to reach terminal velocity, you're home free.

impendingChaos
Apr18-07, 08:24 PM
Ok will check that, Ediss is Energy dissipated

thx!

denverdoc
Apr19-07, 12:28 AM
no sweat, either way problem is soluble:

mv'=-b*v^2+mg.