# Physics teacher has posted log questions

1. Feb 10, 2005

### lguzik

My physics teacher has posted log questions (for fun/frustration)almost every day. Having last had logs about 8 years ago, i have no clue how to solve for any of them. And seeing as how we don't actually use them in class, he won't help us figure them out. If anyone can offer me some solutions to these problems I would be so grateful...

In y=10^x
y=?
x=?

t=AB(1-q/q,)
q=?

z=10^e^x^2
x=?

(q/qsubd)=.2t/sec
q=?

2. Feb 10, 2005

### mathwonk

I had logs 50 years ago and I still know how to do them. Is that supposed to be an excuse? have you still got the book you used?

(people here do not solve your exercises for you, they answer questions that show you have done some thinking.)

3. Feb 10, 2005

### dextercioby

I'm afraid that your equations do not make too much sense,really.E.g.th first is clearly a function (y=y(x) or viceversa x=x(y)),so knowing/giving one means that you can find out the other...
Again for the third,it's the same problem.You'd find "x" as a function of "z"...And nothing more...

Anyway,what do you know about logarithms...?

Daniel.

4. Feb 10, 2005

### HallsofIvy

I presume that by "In", you actually mean "ln", the natural logarithm.
In general, you can't solve one equation for TWO unknowns so the first problem makes no sense.

t= AB((1-q)/q) (the way you have it, the q's would cancel!)
doesn't have anything to do with logarithms.
qt= AB- ABq
qt+ ABq= Ab
q(t+ AB)= Ab

q= AB/(t+AB)

z= 10^(e^(x^2))
so log z= e^(x^2)
so ln(log z)= x^2 and then

x= sqrt(ln(log z))

5. Feb 11, 2005

### lguzik

Thank you for those of you who offered some help. Mathwonk, I suppose you have needed and used your knowledge of logs in the last 50 years. I do not have a math book at all, nor have I needed anything I learned in that class till now. I did not clearly state earlier, my teacher does not give these in relation to our class. They are just little blips he puts off to the side. I was merely asking for some help because they did not make any sense to me, and I would like to know how to solve them. As for Daniels question, the only thing i remember is that logs are the inverse, such that 1/ab=a^-1b^-1 ...My confusion lies in that my teacher seems to be looking for numbers. Again, thanks for some clarity on these.