# Simple function problem

• Nov 21st 2012, 05:59 PM
HenryMerrild
Simple function problem
Hey guys!,
I've been given a test assignment and there's one really simple problem that I've been staring blindly at for some time now:

"The distance that a car can travel on 1 litre of gas at the velocity km/h is given by:
Attachment 25833
In one hour, driving at a constant speed, the car used 7 litre of gas. How fast was it driving?".

Now, I know that this is really simple, but I think my brain turned to mush a few hours ago. I've been asked to calculate v, given a function where the value is distance traveled on 1 litre of gas.
Can anyone give me the first step, please?

Cheers.
• Nov 21st 2012, 06:09 PM
MarkFL
Re: Simple function problem
Since this is a test assignment, did your instructor explicitly state that getting outside help is allowed?
• Nov 21st 2012, 06:25 PM
HenryMerrild
Re: Simple function problem
I think I misused the word "test"! It's not an exam, but a test to prepare us for an upcoming exam and our future homework. So yes, outside help is allowed :)
• Nov 21st 2012, 06:49 PM
MarkFL
Re: Simple function problem
I see, in that case, we know that for constant velocity distance equals velocity times time:

$\displaystyle d=vt$

Now, we also have a way to express the distance from the given function:

$\displaystyle d=7\left(\frac{750v}{v^2+2500} \right)$

Now, equate the two, and solve for $\displaystyle 0<v$, using the given value for $\displaystyle t$.
• Nov 21st 2012, 06:55 PM
HenryMerrild
Re: Simple function problem
I see! Thanks mate! :)
• Nov 21st 2012, 06:58 PM
MarkFL
Re: Simple function problem