GR 8677927796770177 | # Login | Register

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.
$

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!
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.
 JinjunDing2014-10-19 17:30:44 you are not right
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 ali2013-09-01 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 .
saifi_786
2011-08-22 21:00:49
chandanjumech
2011-05-17 06:14:38
I am preparing for gre physics. Is it necessary to be appeared in gre general.
 lee2011-08-16 08:26:16 Yes, Universities ask for both physics GRE as well as general GRE scores.
atp_ch
2010-08-17 05:43:03
test
yosun
2010-06-27 17:47:06
testing123 $\langle my \rangle$
yosun
2010-06-27 17:46:29
testing 123
withuman
2008-04-30 23:08:04
$\frac{a}{b}$
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
abcdefg
2007-06-01 22:53:59
test
BABU G
2007-03-15 21:47:37
how to get a copy of GR8677 and others
 hamood2007-03-24 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.
brandnewus
2007-02-25 03:00:59
this is a test message with $\LaTeX$ and 'quotation's' ... and a complicated equation like $\frac{\sum^\infty_n x_n^2}{\sqrt{x+\gamma}}$
eltha
2006-12-17 09:19:34
is there any way i can get a copy of the test: GR8677, GR0177, GR9677, GR9277?

 seba2406982006-12-18 01:56:11 Yes, could you tell s how to get hold of the tests GR8677, GR0177, GR9677 and GR9277?
 yosun2007-02-21 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.
 yosun2007-02-21 17:37:25 yeah, and will also redesign this site, perhaps..
 yosun2007-02-25 01:47:35 ok, the GR9277 original questions have been posted!
 kainnat2009-02-17 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
 kainnat2009-02-17 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.
eltha
2006-12-17 09:13:57
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.
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?
asm3j
2005-11-10 06:32:30
is there any way i can get a copy of this test?

 yosun2006-01-13 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
asm3j
2005-11-10 06:32:05
jet
2005-11-08 11:18:04

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}\$ $\frac{a}{b}$