Homework Help: Energy Dissipation in Drag

1. Apr 18, 2007

impendingChaos

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.

2. Apr 18, 2007

denverdoc

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.

3. Apr 18, 2007

impendingChaos

Ok will check that, Ediss is Energy dissipated

thx!

4. Apr 18, 2007

denverdoc

no sweat, either way problem is soluble:

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