# Physics question
**URL:** https://forums.speedlife.net/t/physics-question/73294
**Category:** NYSpeed Off Topic
**Created:** [September 9, 2009, 6:45pm UTC](https://forums.speedlife.net/t/physics-question/73294 "2009-09-09T18:45:28Z")
**Posts on this page:** 11
**Page:** 1
### Author:  [@943kgt](https://forums.speedlife.net/u/943kgt)
#### Post date: [September 9, 2009, 6:45pm UTC](https://forums.speedlife.net/t/physics-question/73294/1 "2009-09-09T18:45:28Z")
Ok all you engineers and smart people I have a question that I just can’t seem to get right. So if you would please help me out:
An electron moving along the _x_ axis has a position given by _x_ = 13 _te_^-2.5t m, where _t_ is in seconds. How far is the electron from the origin when it momentarily stops?
Pretty much I’ve figured out that the velocity is the derivative of that function and when the electron stops its velocity is zero. So figure out the derivative and set it equal to zero and solve for t. There is a chain rule and a product rule I believe but its not working out. My calculus is pretty rusty and i’ve got one more attempt at this online question. Thanks in advance!
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### Author:  [@travisn](https://forums.speedlife.net/u/travisn)
#### Post date: [September 9, 2009, 6:56pm UTC](https://forums.speedlife.net/t/physics-question/73294/2 "2009-09-09T18:56:50Z")
using mathXL? click 'show me an example"
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### Author:  [@943kgt](https://forums.speedlife.net/u/943kgt)
#### Post date: [September 9, 2009, 6:58pm UTC](https://forums.speedlife.net/t/physics-question/73294/3 "2009-09-09T18:58:42Z")
wiley plus
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### Author:  [@Willybeen](https://forums.speedlife.net/u/Willybeen)
#### Post date: [September 9, 2009, 7:00pm UTC](https://forums.speedlife.net/t/physics-question/73294/4 "2009-09-09T19:00:16Z")
buahahahahahhahahaa.
that is all i have to offer. good luck buddy.
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### Author:  [@scsilver2](https://forums.speedlife.net/u/scsilver2)
#### Post date: [September 9, 2009, 7:17pm UTC](https://forums.speedlife.net/t/physics-question/73294/5 "2009-09-09T19:17:46Z")
> [@943kgt](#):
>
> wiley plus
The WORST learning aid in the history of the universe.
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### Author:  [@943kgt](https://forums.speedlife.net/u/943kgt)
#### Post date: [September 9, 2009, 7:23pm UTC](https://forums.speedlife.net/t/physics-question/73294/6 "2009-09-09T19:23:48Z")
> [@scsilver2](#):
>
> The WORST learning aid in the history of the universe.
I joined the facebook group “I hate wiley plus” after the first question, it fucking blows…
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### Author:  [@RedGoober4Life](https://forums.speedlife.net/u/RedGoober4Life)
#### Post date: [September 9, 2009, 7:29pm UTC](https://forums.speedlife.net/t/physics-question/73294/7 "2009-09-09T19:29:09Z")
x(0.4) = 1.91297 m
dx/dt = 13 \* exp (-2.5t) - 32.5t \*exp(-2.5t)
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### Author:  [@943kgt](https://forums.speedlife.net/u/943kgt)
#### Post date: [September 9, 2009, 7:37pm UTC](https://forums.speedlife.net/t/physics-question/73294/8 "2009-09-09T19:37:36Z")
I am a fucking retard i got .4 but didnt substitute back into the equation…did all the complicated shit and couldnt plug it in! Thanks!
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### Author:  [@Jack](https://forums.speedlife.net/u/Jack)
#### Post date: [September 9, 2009, 7:50pm UTC](https://forums.speedlife.net/t/physics-question/73294/9 "2009-09-09T19:50:09Z")
goobs is teh smrt.
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### Author:  [@RedGoober4Life](https://forums.speedlife.net/u/RedGoober4Life)
#### Post date: [September 9, 2009, 8:18pm UTC](https://forums.speedlife.net/t/physics-question/73294/10 "2009-09-09T20:18:56Z")
> [@943kgt](#):
>
> I am a fucking retard i got .4 but didnt substitute back into the equation…did all the complicated shit and couldnt plug it in! Thanks!
haha i used to do the some thing for these homeworks.
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### Author:  [@Willybeen](https://forums.speedlife.net/u/Willybeen)
#### Post date: [September 10, 2009, 4:30am UTC](https://forums.speedlife.net/t/physics-question/73294/11 "2009-09-10T04:30:37Z")
:tup: