# Modelling help required desperately!

1. Dec 21, 2007

### magicuniverse

1. The problem statement, all variables and given/known data

I need some help with all of the questions in the attatchment but would love it if you could provide some help with the first question please.

2. Relevant equations

In the file.

3. The attempt at a solution

Dont be silly, I dont have a clue. If I could do it I wouldnt be posting here!

#### Attached Files:

• ###### F31ARME1-07.pdf
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2. Dec 21, 2007

### malawi_glenn

I dont like your tone: "Dont be silly"

3. Dec 21, 2007

### magicuniverse

Well I was talking to the computer and trying to be lighthearted. Sorry if I really offended you.

4. Dec 21, 2007

### HallsofIvy

Staff Emeritus
I would also point out that there is an enormous gap between "I don't have a clue" and "If I could do it". What you have posted appears to be a test (perhaps a practice test) for a class in mathematical modelling. Surely, you have had some instruction in this?

Problem 1 appears to be a matter of replacing some terms in the formula for Q by their expression as a function of T, the temperature. That is, the formula for Q involves viscosity $\eta$; $\eta$ itself is a function of $\overline{\nu}$ which, in turn "is proportional to the square root of temperature". Q also is proportional to the radius, R, to the fourth power and (1/R) (dr/dT) is a constant.

For problem 2, you are given how the Velocity depends upon position, x, V(x).
Use F= ma. a= dV/dt= (dV/dx)(dx/dt)= V dV/dx.

5. Dec 24, 2007

### Shooting Star

V(x) represents the potential here, not velocity.

We don't like that here. If you show a bit of effort, a lot of help will be readily forthcoming. I'll give you some hints anyway.

F = m*(-dV/dx). At equilibrium, F=0, so you can find the value of x.

For plotting the graph, take the derivative and see how it changes signs. Consider how V(x) behaves for fractional values and for x>1. Remember, it’s an even function.

For prob 1, you must have understood by now that what you have to find is dQ/Q in terms of dT.