GR9277 #85



Alternate Solutions 
unoriginal5279 20070411 09:24:43  When short on time (as I always am) I try to avoid calculations whenever possible. If you remember that E= m c + (p c) then you already know that the momentum must be less than the energy, but greater than the difference between the energy and m c . This eliminates all but the correct answer.   Andresito 20060329 15:15:31  You could always use the general equation,
E^2 = (p*c)^2 + (m*c^2)^2
Solve for p having E = 3/2, and m*c^2 = 1/2
to obtain 1.4 as in (C).
Andresito 20060329 15:21:28 
The equation I describe is beter to use since you only ned to take a square root once, and that helps when having larger numbers, see in test 9277 problem 70.

Andresito 20060329 15:24:03 
The equation I describe is beter to use since you only ned to take a square root once, and that helps when having larger numbers, see in test 9277 problem 70.

 

Comments 
EPdropout 20121108 17:12:29  I used T=p/2m=(1)mc, after finding =3
=>p=2m*(2/3)E
=>p=2.0 (MeV^2/c^2)
=>p =1.4 MeV/c   rrfan 20111106 17:41:09  A useful shortcut on these types of relativity problems:
The solution to is the following: .
Even if you don't memorize this, it is straightforward to derive and is often useful on multiple problems, saving some time on the algebra.   dinoco 20101107 07:52:37  You say that "v=2c/3." But since =8/9 then
v should be 2c/3   unoriginal5279 20070411 09:24:43  When short on time (as I always am) I try to avoid calculations whenever possible. If you remember that E= m c + (p c) then you already know that the momentum must be less than the energy, but greater than the difference between the energy and m c . This eliminates all but the correct answer.
apr2010 20100408 12:25:33 
Remarkable

thinkexist 20121012 09:29:49 
This is actually so simple and brilliant I cannot believe I have not thought of this before.

justin_l 20131015 23:50:31 
if something is remarkably brilliant, would it not be more surprising that you *do* think of it?

  Andresito 20060329 15:15:31  You could always use the general equation,
E^2 = (p*c)^2 + (m*c^2)^2
Solve for p having E = 3/2, and m*c^2 = 1/2
to obtain 1.4 as in (C).
Andresito 20060329 15:21:28 
The equation I describe is beter to use since you only ned to take a square root once, and that helps when having larger numbers, see in test 9277 problem 70.

Andresito 20060329 15:24:03 
The equation I describe is beter to use since you only ned to take a square root once, and that helps when having larger numbers, see in test 9277 problem 70.

ramparts 20090806 22:54:12 
Well, it's better to use in problem 70, but I think it's pretty clear that for this question, the E^2 equation takes a lot less calculation than the "official" answer.

GREview 20090830 19:22:53 
It may simplify things to not even think about the 's:
Plugging and , we can solve for .

Albert 20091105 00:32:16 
Hey, I see what you did there, you used the c's in the denominator of the units right along side the values, smart work. Best solution!

 

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