Author Topic: Math Help Request ~ (Read 1106 times) Tweet Share

yejiawen · « **on:** July 04, 2010, 03:13:54 pm »

Can anyone solve the attached question for me please?

I'm stuck on that one.

I've derived it, and subbed in 1 since it's close to 0.9

after that, i'm lost

Thanks in advance!

superflya · « **Reply #1 on:** July 04, 2010, 03:21:48 pm »

so if u derived it and subbed in 1 u should get -1/3.

so ur change in y is approximately ur step size which in this case is -0.1 (difference between 1 and 0.9) multiplied by the value u get when u subbed in 1 after deriving it which was -1/3. after multiplying u get 1/30.

$\frac{1}{\sqrt[3]{0.9}}\approx\frac{1}{\sqrt[3]{1}} + \Delta y$

$1 + \frac{1}{30}$

$\Rightarrow \frac{1}{\sqrt[3]{0.9}}\approx \frac{31}{30}$

yejiawen · « **Reply #2 on:** July 04, 2010, 03:25:44 pm »

^ you genius. LOL I'll reember your karma when I get 50 posts

Thanks heaps!

superflya · « **Reply #3 on:** July 04, 2010, 03:29:01 pm »

no problem

yejiawen · « **Reply #4 on:** July 04, 2010, 03:45:23 pm »

I need help with one more...

brightsky · « **Reply #5 on:** July 04, 2010, 06:24:25 pm »

$T = 2 \pi \sqrt{\frac{l}{g}} = 2\pi \cdot \left(\frac{1}{g} l\right)^{\frac{1}{2}}$

a) $\frac{dT}{dl} = \frac{1}{2} \cdot 2\pi \cdot \left(\frac{1}{g} l\right)^{-\frac{1}{2}} \cdot \frac{1}{g}$

$= \frac{\pi}{g\sqrt{\frac{l}{g}}}$

b) $\delta T \approx \frac{dT}{dl} \delta l$

$\delta T \approx \frac{\pi}{g\sqrt{\frac{1.6}{g}}} \cdot 0.1$

$\delta T \approx \frac{0.1\pi}{g\sqrt{\frac{1.6}{g}}}$

pooshwaltzer · « **Reply #6 on:** July 04, 2010, 06:31:27 pm »

T = 2(pi)(l/g)^0.5

let u = l/g; du/dl = 1/g

T = 2(pi)(u)^0.5; dT/du = (pi)(u^-0.5)

dT/dl = (dT/du)*(du/dl) = (pi)/{g((l/g)^0.5)}

yejiawen · « **Reply #7 on:** July 04, 2010, 09:53:11 pm »

I see you guys have the same answer, concluding that the answer at the back of the book is probably incorrect. However, have a look at the worked out solution book :S

I don't doubt you guys, I'm doubting the book. It has so much errors!

brightsky · « **Reply #8 on:** July 04, 2010, 09:59:33 pm »

It's not wrong, it's just simplified. :p

a) $\frac{\pi}{g\sqrt{\frac{l}{g}}} = \frac{\pi}{\sqrt{\frac{lg^2}{g}}} = \frac{\pi}{\sqrt{lg}}$

b) $\frac{0.1\pi}{g\sqrt{\frac{1.6}{g}}} = \frac{0.1\pi}{\sqrt{\frac{1.6g^2}{g}}} = \frac{0.1 \pi}{\sqrt{1.6g}} = \frac{\pi}{10\sqrt{1.6g}} = \frac{\pi}{\sqrt{160g}} = \frac{\pi}{4\sqrt{10g}}$

yejiawen · « **Reply #9 on:** July 04, 2010, 10:06:39 pm »

(pi)/{g((l/g)^0.5)}

is simplified to (pi)/{(gl)^1/2} ? O_________O

*mind my brain fart atm LOL

brightsky · « **Reply #10 on:** July 04, 2010, 10:09:17 pm »

See above (post edited).

yejiawen · « **Reply #11 on:** July 04, 2010, 10:12:16 pm »

^ THANK YOU LOL

yejiawen · « **Reply #12 on:** July 04, 2010, 10:14:11 pm »

^ I finally understand LOL Thanks

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