GREPhysics.NET: GR8677 #1

GR8677 #1

Problem

GREPhysics.NET Official Solution

Alternate Solutions

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 $v_0$ .

Alternate Solutions

There are no Alternate Solutions for this problem. Be the first to post one!

Comments

withuman
2008-04-30 23:08:04

$\frac{a}{b}$

Reply to this comment

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

Reply to this comment

abcdefg
2007-06-01 22:53:59

test

Reply to this comment

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

Reply to this comment

brandnewus
2007-02-25 03:00:59

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

Reply to this comment

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!

Reply to this comment

eltha
2006-12-17 09:13:57

Reply to this comment

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.

Reply to this comment

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?

Reply to this comment

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

Reply to this comment

asm3j
2005-11-10 06:32:05

Reply to this comment

jet
2005-11-08 11:18:04

Reply to this comment

Post A Comment!

Bare Basic LaTeX Rosetta Stone
LaTeX syntax supported through dollar sign wrappers $, ex., $\alpha^2_0$ produces $\alpha^2_0$ .
type this...	to get...
$\int_0^\infty$	$\int_0^\infty$
$\partial$	$\partial$
$\Rightarrow$	$\Rightarrow$
$\ddot{x},\dot{x}$	$\ddot{x},\dot{x}$
$\sqrt{z}$	$\sqrt{z}$
$\langle my \rangle$	$\langle my \rangle$
$\left( abacadabra \right)_{me}$	$\left( abacadabra \right)_{me}$
$\vec{E}$	$\vec{E}$
$\frac{a}{b}$	$\frac{a}{b}$

The Sidebar Chatbox...
Scroll to see it, or resize your browser to ignore it...

Chat Archives | Delete left banner ad | Donate

(Click to view chat.)

Hate being Anonymous? Login or Register

Upgrade to Poser 7 Now

Huge Textbook Selection, Low Prices – Phat Campus.

All-Solutions List | Latest Comments | Unanswered Questions (Cries for Help!) |::| About

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.

Bare Basic LaTeX Rosetta Stone