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162956 No.10439   [Delete]   [Edit]  [Reply]

Hello there physicists, I have a question;

A 0.50 kg wooden block is dropped from a height of 15.0 m. At what height must a 005.0 kg bullet traveling upward strike the block in order to momentarily stop its fall? Assume that the time required for the bullet to come to rest is in the block is negligibly short and that the bullet travels with a speed of 320 m/s immediately before striking the block.

Does anybody know the solution?

10 posts and 2 images omitted. Click Reply to view.
>> No.10487   [Delete]   [Edit]

I don't like my answer because it does not seem right. I have 14.995 m.

It is still mathematically possible, at least, for the formula associated with inelastic collisions for the final velocity of the two objects to be a zero vector. It is clear that we started out with more kinetic energy prior to impact than after, since before, we had 0.5*m_bullet*|v_bullet|^2 + 0.5*m_block*|m_block|^2 and afterwards, we have, as you said, 0. However, kinetic energies cannot "cancel out" the way forces and fields do. What occurred was a dissipation of kinetic energy as work deforming the block and heat emitted due to friction. I submit that this does not tell us what the relationship between the kinetic energy of each object is, but assuming a completely elastic collision (which this problem describes), we can set the right side of the respective momentum equation to a zero vector and proceed from there.

But then, like I said, I think I went wrong somewhere with my solution.

Last edited 10/01/12(Tue)02:30.

>> No.10502   [Delete]   [Edit]

>>10487
I argue that the kinetic energy of the brick and the bullet have to be equal to one another or otherwise they wouldn't cancel each others motion at the collision.

this leads me to believe that just before the moment of impact the bullet would have Ek=0.5*0.005*320^2=256J of energy. the brick needs to pick up speed while falling until it's fast enough to have equal kinetic energy.

v=sqrt(256/(0.5*5))=10.12 m/s(rounded)
v=gt so 10.12/9.81=1.03 s (rounded)

after 1.03 seconds the brick goes fast enough.
d=0.5gt^2 so d=0.5*9.81*1.03^3=5.20 meter (rounded)

so, the height is around 15-5.20=9.80 meters

Last edited 10/01/13(Wed)04:20.

>> No.10512   [Delete]   [Edit]

sup all

>> No.10573   [Delete]   [Edit]

Forgot to submit my comment earlier.

Momentum is always conserved in a system with no outside work done to it; kinetic energy, however, is not conserved in an inelastic collision.

Why exactly, then, would the inelastic collision equation not apply?

>> No.10575   [Delete]   [Edit]

if it were an inelastic collision the bullet wouldn't dig inside the brick and get stuck there, but the 2 would bounce right off like 2 approaching snooker balls. consider newtons cradle: http://upload.wikimedia.org/wikipedia/commons/d/d3/Newtons_cradle_animation_book_2.gif)
only in this case would momentum be preserved. a true completely inelastic collision however does not exist in real life.

>>10512
yo.

Last edited 10/01/15(Fri)20:21.



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115529 No.9517   [Delete]   [Edit]  [Reply]

I know some people here on Desuchan have pets, so let's see them. This is my bird, I don't have a name for him yet.

20 posts and 12 images omitted. Click Reply to view.
>> No.9751   [Delete]   [Edit]

>>9750
No, but close. She's a Blue-Point Siamese.

>> No.10421   [Delete]   [Edit]
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1458015

This is my kitty :3 Her name is Oreo and she's awesome.

>> No.10423   [Delete]   [Edit]

>>10421
Oh man, I can't play guitar hero laying down like that. Your cat's got skillz!

>> No.10429   [Delete]   [Edit]

>>10421
What difficulty is she playing on?

>> No.10431   [Delete]   [Edit]

>>10429

Expert. She's better than me :(



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10170 No.10399   [Delete]   [Edit]  [Reply]

http://theseoultimes.com/ST/?url=/ST/db/read.php?idx=7333

baby soup in china

surely this is a joke

>> No.10400   [Delete]   [Edit]

Looks like a FOX News kind of article...

>> No.10408   [Delete]   [Edit]

Dogs too
http://news.bbc.co.uk/2/hi/7501768.stm

>> No.10409   [Delete]   [Edit]

http://www.snopes.com/horrors/cannibal/fetus.asp
http://www.prisonplanet.com/baby_eating_art_show_sparks_upset.html
http://en.wikipedia.org/wiki/Zhu_Yu_(artist)

>> No.10411   [Delete]   [Edit]

>>10409
I like this guy.



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251549 No.10405   [Delete]   [Edit]  [Reply]

Does it work well for you guys, or does it appear as if the upload does not get updated on the confirmation page?



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151580 No.9717   [Delete]   [Edit]  [Reply/Last 50]

I've just have been banned from 4chan for the following reason: "no".

have you guys gotten one getter or worse?

53 posts and 23 images omitted. Click Reply to view.
>> No.10324   [Delete]   [Edit]

>>10322
/a/ is a sea of trolls and MOEfags.

>> No.10357   [Delete]   [Edit]

>>10290
As a regular on 420chan and on their boards, i can say that i am a fan of him

>> No.10363   [Delete]   [Edit]

>>10357

I love netjester. So much Kirtner banned me for fucking round with him for a day :D

>> No.10378   [Delete]   [Edit]

>>9717
I got banned from 7chan for the reason "no"

>> No.10383   [Delete]   [Edit]

>>10378
7chan is better than 4chan in many ways, but they still have their fare share of mistakes.

For example, I've been banned a few times for some bullshit reasons and never once got the chance to appeal any of them.

Anything you can think of that might've earned it?



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430837 No.10229   [Delete]   [Edit]  [Reply]

comic thread go

1 posts omitted. Click Reply to view.
>> No.10234   [Delete]   [Edit]
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323411

:|

>> No.10267   [Delete]   [Edit]
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591618
>> No.10282   [Delete]   [Edit]

>>10234

>chaos was fucked

I lol'd heartily.

>> No.10307   [Delete]   [Edit]
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109114
>> No.10364   [Delete]   [Edit]
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109227


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66629 No.9464   [Delete]   [Edit]  [Reply]

My photoz...

13 posts and 13 images omitted. Click Reply to view.
>> No.9548   [Delete]   [Edit]
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34371

>>9480

>> No.9949   [Delete]   [Edit]
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32404

ecksdee

>> No.10360   [Delete]   [Edit]
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33124

http://minkara.carview.co.jp/userid/534263/blog/16425130/

>> No.10361   [Delete]   [Edit]
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36511

http://en.wikipedia.org/wiki/Washinomiya_Shrine

The August 2007 issue of the Newtype magazine ran an article on the various locales featuring in the popular anime and manga Lucky Star, and provided directions on how to reach these places from the otaku hotspot Akihabara, including the Washinomiya Shrine which had its torii shown in the opening sequence and featured the Hiiragi sisters working as miko in the anime.

Shortly afterwards, massive otaku pilgrimages to the shrine became the most widely reported consequence of the feature's publication. It became a place teeming with photographers trying to replicate scenes from the anime, cosplayers wandering around, and prayer plaques ridden with anime drawings and strange prayers like "Konata is my wife".

>> No.10362   [Delete]   [Edit]
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45818
>The head of the shrine raised concerns that the visitors were worshiping "deities" other than the shrine's own.

Oh how I lol'd



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59888 No.10332   [Delete]   [Edit]  [Reply]

Why can't real girls be like Kobato? T_T

>> No.10333   [Delete]   [Edit]

Because they're pig disgusting 3D

>> No.10344   [Delete]   [Edit]

>>10332

Why can't we post this in just one place? Kobato would have just posted in one place.

>> No.10355   [Delete]   [Edit]

Why can't real threads be about Kobato?

>> No.10359   [Delete]   [Edit]
File: 1262708070741.jpg -(27.4 KiB, 600x339) Thumbnail displayed, click image for full size.
28102

Kobato is real uuu uuu uuu



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20257 No.10327   [Delete]   [Edit]  [Reply]

THIS JUST IN:

EUROPEANS CAN'T DRIFT FOR SHIT

http://www.youtube.com/user/wynne1975#p/a/u/1/7MPRmOUxRMY

Also, general amusing car accident videos and stories, I guess.

>> No.10334   [Delete]   [Edit]
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2047120
>car accident videos and stories

Well, I don't have videos or stories, but I do have gifs, would that be ok?

>> No.10336   [Delete]   [Edit]

ITT: /gif/



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1677817 No.10202   [Delete]   [Edit]  [Reply]

What's your score, desuchan?

12 posts and 2 images omitted. Click Reply to view.
>> No.10293   [Delete]   [Edit]

>>10292
Why don't you just tell us your achievements DetectiveShinku?

>> No.10294   [Delete]   [Edit]
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1868385
>> No.10300   [Delete]   [Edit]
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1828756

67

>> No.10306   [Delete]   [Edit]

behind seven proxies, ambidexterous, anger management, anti-depressant, backstabber, behind enemy lines, big belly big lovin, biodegradable, bullseye, company ink, corruption, dodged it!, duracell, early bird, endurance fap, endurance test, family shot, fap and dump, feels good man, friction burn, green thumb, hot fire, hot nights, i buy it for the articles, imagination mode, in recent news, iron man, iron will, jetson! you're fired!, kodak moment, long shot, messmaker, mount vesuvius, multi shot, music to my ears, ninja-fap, no hands, quickshot, rageeee, rebound, safety, self sufficiency, seppuku, so ronery, tastes like chicken, the good student, this is so wrong, tickle me elmo, trap fap, tresfapping, two birds one stone, v for vendetta, voyeur, wet willy, work with what ya got

>> No.10313   [Delete]   [Edit]

>>10292
agreed! i try my best to only fap to doll joints and only when in the best of mood while sipping tea in the comfort of my own home!



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