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Old 08-28-2009, 07:04 PM   #1
TeLe
Question Anyone good at calculus based physics? I need some help

I have these two homework problems that are a real pain in my butt and I have 2 hours and 50 minutes (10pm EST) left to complete them before the homework needs to be submitted. If anyone could help me attempt to solve the problems ill love you forever. Heres the two problems. I have no clue where to start for the first one and in the second I derived but i got the wrong answer and don't know what I did wrong.

1. Gold, which has a density of 19.32 g/cm^3, is the most ductile metal and can be pressed into a thin leaf or drawn out into a long fiber. (a) If a sample of gold with a mass of 4.831 g, is pressed into a leaf of 4.562 μm thickness, what is the area (in m^2) of the leaf? (b) If, instead, the gold is drawn out into a cylindrical fiber of radius 2.600 μm, what is the length (in m) of the fiber?

2. Water is poured into a container that has a leak. The mass m of the water is given as a function of time t by m = 5.4t^0.8 - 3.4t + 21, with t ≥ 0, m in grams, and t in seconds. (a) At what time is the water mass greatest, and (b) what is that greatest mass? In kilograms per minute, what is the rate of mass change at (c) t = 1.8 s and (d) t = 5.0 s?

thanks in advance.
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Old 08-28-2009, 07:05 PM   #2
Mad-Mike

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Default Re: Anyone good at calculus based physics? I need some help

lol homework just sack it..
nice 4th post though :P

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Old 08-28-2009, 07:06 PM   #3
TeLe
Default Re: Anyone good at calculus based physics? I need some help

Hahaha i know its lame. Cutting into my PR time
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Old 08-28-2009, 07:09 PM   #4
Mad-Mike

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Default Re: Anyone good at calculus based physics? I need some help

haha sorry lol gettin back to the topic I do not have a clue mate, best option is Google

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Old 08-28-2009, 07:12 PM   #5
TeLe
Default Re: Anyone good at calculus based physics? I need some help

No problem bro. Yeah I have been staring at these 2 problems for practically 7 hours now and googled everything I could think of. This is my act of desperation hahaha.
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Old 08-28-2009, 07:26 PM   #6
DankE_SPB
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Default Re: Anyone good at calculus based physics? I need some help

Quote:
Originally Posted by TeLe View Post

1. Gold, which has a density of 19.32 g/cm^3, is the most ductile metal and can be pressed into a thin leaf or drawn out into a long fiber. (a) If a sample of gold with a mass of 4.831 g, is pressed into a leaf of 4.562 μm thickness, what is the area (in m^2) of the leaf? (b) If, instead, the gold is drawn out into a cylindrical fiber of radius 2.600 μm, what is the length (in m) of the fiber?
does "leaf" means it is a cylinder with 4.562 μm thickness? if so i think i have something to share with you


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Old 08-28-2009, 07:47 PM   #7
ralfidude

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Default Re: Anyone good at calculus based physics? I need some help

If anybody knows differential equations, it can help with his second question. I remember doing a very similar problem, but i cannot remember what the formula for that was. I wish i could help dude, im starting Engineering based Calc III now.... im in trouble...

Try Yahoo answers, they always have some bloke who answers rather fast.

Good luck


PS: dont know if it helps u any, but on the second question take the derivative of that equation to get its velocity, and derive that again to get the acceleration. Maybe that can point you towards something.

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Old 08-28-2009, 07:55 PM   #8
DankE_SPB
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Default Re: Anyone good at calculus based physics? I need some help

Quote:
Originally Posted by ralfidude View Post
PS: dont know if it helps u any, but on the second question take the derivative of that equation to get its velocity, and derive that again to get the acceleration. Maybe that can point you towards something.
you're on the right way with this for sure, its pretty standard task, but it was ~3 ago when i solved such things so my knowledge needs some refresh
though the first task is pretty simple


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Old 08-28-2009, 07:56 PM   #9
TeLe
Default Re: Anyone good at calculus based physics? I need some help

No the leaf is totally different :/ It is suppose to mean it is flat i guess.
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Old 08-28-2009, 07:59 PM   #10
DankE_SPB
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Default Re: Anyone good at calculus based physics? I need some help

Quote:
Originally Posted by TeLe View Post
No the leaf is totally different :/ It is suppose to mean it is flat i guess.
ehh, them why there is
Quote:
pressed into a leaf of 4.562 μm thickness
if its flat they wont give you thickness right?


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