GREPhysics.NET: GR8677 #1

GREPhysics.NET

GR8677 #1

Problem

GREPhysics.NET Official Solution

Alternate Solutions

Verbatim question for GR8677 #1

Mechanics $\Rightarrow$ }Newtonian

This problem can be translated into an equation:

$m\ddot{x}=-k\dot{x}-mg. <br />$

Note that the sign is compensated for. $\dot{x}$ is positive going up (so that $-k\dot{x}$ acts in the same direction as gravity), and it is negative going down (acting in the opposite direction of gravity).
\par

(A) $\ddot{x}\neq g \forall t$ because $\ddot{x}=\frac{1}{m}\left(-k\dot{x}-mg\right)$

(B) True. $\dot{x}=0$ at the top. Thus, plug that into the equation in described in (A) and get $\ddot{x}=-g$

(C) $\ddot{x}=\frac{1}{m}\left(-k\dot{x}-mg\right)$ could be greater than $g$ , especially when $\dot{x}$ is positive in sign.

(D) The wind friction ( $-k\dot{x}$ ) term would change sign when going downwards. (See the Note above.) Thus, the equation of motion presented above would be different in sign going down and up. (Also, one could argue that after the force of wind friction acts, to conserve energy, kinetic energy must lessen in the final energy sum. Thus, the final velocity can't be the same as $v_0$ . Or, intuitively, one could see friction as a symmetry breaker, viz., the ideal parabolic path is disturbed in such a way that the end velocity changed.)

(E) Since the force other than gravity is a frictional force, which, by definition, slows down the object, the final velocity has to be less than $v_0$ .

See below for user comments and alternate solutions!

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Comments

Hopeful
2017-12-26 16:23:08

Oops. I see your post is recent. Most of the posts I've seen on here are several years old so I was assuming.

Go back to school. This test is too difficult to take without the background. I actually did just that myself. Got a BA in visual art and went back and basically started over (except didn't have to tak gen Ed again). It'll take a few years but 5 years from now 5 years will have passed regardless.

Good luck!

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sanket narharshettiwar
2017-09-05 10:09:25

if you are not having any physics background but still want to pursue physics GRE then any suggestion?

flatearther
2017-11-23 17:07:31

The earth is flat! That's why is doesn't make sense! One thing to know about math, is you can lie in math and no one will know the wiser unless they go check it in real life. Does an empty cup equal a full cup? well in math it does, but in real life you drinking a cup of milk doesn't equal to you drinking a cup of air. Youtube search "Edward Hendrie" and watch the playlist with 26 videos in it, then you will know about how Einstein is a fraud! also youtube search "WLC Videos flat earth jesuits". This problem with newton and physics is that it is a lie, you can lie with math all you want!

flatearther
2017-11-23 17:10:35

https://www.youtube.com/watch?v=pNe1wWeaHOU&list=PLYI8318YYdkCsZ7dsYV01n6TZhXA6Wf9i

Hopeful
2017-12-26 16:11:59

Hahahaha! I think I'll take my chances and continue to study for this test! Hahahahah

Hopeful
2017-12-26 16:15:28

To the OP, it took 3 to 4 years to learn this material in the first place. I personally don't think I could have done it on my own in that time frame. I know your post is several years old but hopefully you went back to school and took the under grad physics sequence otherwise it's impossible to take this test.

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nomdaq
2014-07-20 16:23:49

the solution is not clear to me. kindly tell me the net force acting own the stone. why we have taken -mg here.

JinjunDing
2014-10-19 17:30:44

you are not right

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Answered Question!

drs2872
2013-08-08 22:20:58

How should I start preparing for GRE Physics test, I just have two months in hand? Which study material should I refer to get the exact depth of syllabus?

iskhar ali
2013-09-01 02:54:26

I have also apply for the GRE physics see and study the outline of gre and old papers of gre physics and memorize physics formulas .

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saifi_786
2011-08-22 21:00:49

can I download the answers of these books?

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chandanjumech
2011-05-17 06:14:38

I am preparing for gre physics. Is it necessary to be appeared in gre general.

lee
2011-08-16 08:26:16

Yes, Universities ask for both physics GRE as well as general GRE scores.

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atp_ch
2010-08-17 05:43:03

test

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yosun
2010-06-27 17:47:06

testing123 $\langle my \rangle$

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yosun
2010-06-27 17:46:29

testing 123

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withuman
2008-04-30 23:08:04

$\frac{a}{b}$

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shashiprakash
2007-07-23 23:38:47

shouldnt be the sign of mg be taken as positive in the equation which has been formed in the solution......if we see in terms of force,than ( m*g-k*v) shows us that effective force is reduced hence the there will be less acceleration than g...what are the standard sign conventions for taking g force

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abcdefg
2007-06-01 22:53:59

test

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BABU G
2007-03-15 21:47:37

how to get a copy of GR8677 and others

hamood
2007-03-24 17:13:27

If you go to this link http://www.physics.ohio-state.edu/undergrad/ugs_gre.php

and scroll down to the very end, you will find the 4 released gre exams.

hamood
2007-03-24 17:15:49

http://www.physics.ohio-state.edu/undergrad/ugs_gre.php

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brandnewus
2007-02-25 03:00:59

this is a test message with $\LaTeX$ and 'quotation's' ... and a complicated equation like $\frac{\sum^\infty_n x_n^2}{\sqrt{x+\gamma}}$

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Typo Alert!

eltha
2006-12-17 09:19:34

is there any way i can get a copy of the test: GR8677, GR0177, GR9677, GR9277?

seba240698
2006-12-18 01:56:11

Yes, could you tell s how to get hold of the tests GR8677, GR0177, GR9677 and GR9277?

yosun
2007-02-21 14:16:04

Yes, I'll post the original problems here next to the problems in the next few days or weeks. I know how hard it is to get a copy of the problems if you don't know the right people (and can't afford the thousand-dollar eBay bids...) Hopefully, that'd help.

yosun
2007-02-21 17:37:25

yeah, and will also redesign this site, perhaps..

yosun
2007-02-25 01:47:35

ok, the GR9277 original questions have been posted!

kainnat
2009-02-17 10:12:53

is there any way I can get a copy of the test:
GR86-2
GR90-16
GR91-17
GR91-18
GR91-19
GR92-1
GR92-2

kainnat
2009-02-17 10:14:35

I am preparing for general and physics gre . I got a lot of information for physics but not for general. so anybody will help me . Thanks.

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eltha
2006-12-17 09:13:57

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x111
2006-10-29 00:03:38

try http://www.hcs.harvard.edu/~twiki/bin/view.cgi/SPS/PhysicsGREResources?rev=1.5 />
GRE papers and a lot of physics study materials are also there.

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caseycsh
2006-06-06 19:59:25

I tried to browse thru the website of Brandeis but couldn't log into it. How should I get a copy of the test, Yosun?

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asm3j
2005-11-10 06:32:30

is there any way i can get a copy of this test?

yosun
2006-01-13 14:27:15

Brandeis has all 4 released GRE Physics exam years available online:

http://www.physics.brandeis.edu/undergraduate/GRE_physics/GRE.html

FYI: This includes GR8677, GR0177, GR9677, GR9277

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asm3j
2005-11-10 06:32:05

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jet
2005-11-08 11:18:04

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This site is not affiliated with ETS, nor is it officially endorsed (yet) by ETS. This site is the work of an individual named Yosun Chang. The solutions, sans user comments and ETS questions, are © 2005 by Yosun Chang except where noted. All rights reserved. / The comments appending particular solutions are due to the respective users. / Educational Testing Service, ETS, the ETS logo, Graduate Record Examinations, and GRE are registered trademarks of Educational Testing Service. The examination questions are © 1997 and © 2001 by ETS.