Finding volume of Revolution help

N

NiCeBoY

New member
Joined
Aug 30, 2008
Messages
29
Determine the volume of the solid obtained by rotating the region bounded by the curves y=5x and y=x^2 about the x-axis.

What i know is that this formula should be used.But i dont know how to apply it..

Formula.JPG

Please me help me out..i have only 2 hours left for this assignment.
thanks.
 
Less than 45 minutes to go. :shock: Okay, you're tugging at my heartstrings ...

I'm not sure if your formula is correct, but it seems right to me. Some fuzzy math in my brain allowed me to scrawl the following. (I'm thinking of disks surrounding the x-axis, and the surface of each disk is Pi * radius squared, and all of these disks added together make a volume.)

Can you take it from here? I don't have time right now to verify by checking out those links that I provided you earlier ... I also don't have time to refresh my memory on the calculation of the integral ... I only have time to setup the integral ... I hope that it's correct ... use at your own risk! :twisted:

intsldrev.JPG


~ Mark
 
Just as an aside, you can also use shells and get the same result.

It's a nice check if you can mange both.

\(\displaystyle 2{\pi}\int_{0}^{25}y(\sqrt{y}-\frac{y}{5})dy\)
 
Hello,
I have worked this question on finding the volune of revolution.. but i think there is something wrong..
I have posted the question + my works up to the answer.

Can anyone check it and let me know if its good please?
I have to submit it in 12 hours time.

The question:
Q4.JPG


My answer:
volums.JPG



Should i use this formula ?if yes how do i apply it here...

Formula:
Formula.JPG


Thanks in advance..
 
Please tell us the differences between the method you used versus the method suggested by the formula.
 
i kniw its seems to be almost the same..
but someone get this as answer... and am not getting this:

ans.JPG


=1308.997

and mine is diferent..
 
NiCeBoY said:
i kniw its seems to be almost the same..
but someone get this as answer... and am not getting this:

ans.JPG


=1308.997

and mine is diferent..
Click to expand...

The first line of this (later)image - is repeated in your work.

From there on - it is just calculator work. Someone - somewhere slipped. It is not worth more than 5% of the grade for the problem (in my estimation). If you have time and desire - dig in.

Anyway - your numerical answer is incorrect. The answers (number without pi) were 1250 apart - should give you a clue.
 
If you have not found your mistake yet - look at your solution. Look at the third line from the bottom and the second line from the bottom.

You zigged (add) - when you should have zagged (subtract).

But as I said before - this is a very minor mistake.
 
You must log in or register to reply here.
Top