tdl17 20190105 22:45:55  You can also use dimensional analysis. Whatever that goes into the arc tangent should be purely numerical without any units, and the only answer where this happens is choice A. Vq cancels with mv^2 because they both have units of Joule. L cancels with d because they both have units of length.  
deneb 20181008 04:12:51  You have to divide both sides by , and since is just the original velocity given in the problem, that\\\\\\\'s how you get in the denominator  
allenabishek 20170803 19:29:24  Why is it that in the solution to find dy, the first term is ignored ?? the kinematic equation is actually y = v0t + 0.5at^2. why is the first term ignored?  
dipanshugupta 20170322 14:15:07  Well A looked more beautiful.  
hooverbm 20121102 09:15:49  Found a super fast way of doing this.
The charge is obviously acted upon by a force due to the electric field.
For parallel plates, the acceleration due to this force only acts along the ydirection. We know:
F = qE (V = Ed > E = V/d)
ma = qV/d
a = qV/md
The angle of deflection should be proportional to this term, leaving only answer A  
soloeclipse 20101104 16:31:02  All of the answers are dimensionless.
SonOfHam 20101112 22:21:52 
+1

kevintah 20151012 19:03:36 
lol, this sucks!

 
shjung84 20101014 21:55:12  See dimension
The only possible choice is A of which argument indicates no dimension.  
Moush 20100915 18:11:51  For a completely unphysical approach, see below. To actually learn something, see other posts.
I got this via simple guessing strategy.
(L/d) shows up in 3 answers; and only once, eliminating C and E.
Vq shows up twice in the remaining answers; 2Vq once, eliminating D.
just looks wrong, eliminating B.
ryanmes 20181024 01:19:02 
I did the same thing... it works

 
dstahlke 20091009 10:57:43  The diagram threw me off here... The deflection of the final velocity is but the dotted lines on the diagram form a triangle suggesting they want which I think would be equal to . That wasn't one of the options so in this case I suppose guessing the nearest answer would work.  
haro 20070413 04:25:01  It is simplier to think of tan =
Jeremy 20071015 12:01:19 
I agree. From use , , and finally, the equation you gave: .

walczyk 20110405 13:27:12 
this works well except i don't see where the comes in?

 
yosun 20051109 14:42:33  tachyon: thanks for the typoalert; it has been corrected.  
tachyon 20051109 13:36:53  typothe correct answers is A  