Register to reply

Ek0-Ek1 > 0

by May11
Tags: ek0ek1
Share this thread:
May11
#1
Apr7-12, 03:32 PM
P: 8
Hi there,
I need your help to prove the following, please:

Ek0-Ek1>0

Thanks in advance. (:
Phys.Org News Partner Physics news on Phys.org
Engineers develop new sensor to detect tiny individual nanoparticles
Tiny particles have big potential in debate over nuclear proliferation
Ray tracing and beyond
micromass
#2
Apr7-12, 03:41 PM
Mentor
micromass's Avatar
P: 18,334
Try to prove that Ek1-Ek0<0

Seriously, if you don't explain your notation, then we can't help obviously.
May11
#3
Apr7-12, 04:18 PM
P: 8
Ek0 is the initial kinetic energy that an object possesses.
Ek1 is the eventual kinetic energy that an object possesses.

Try to prove that Ek0-Ek1 (energy loss) equals a positive value.

May11
#4
Apr7-12, 04:26 PM
P: 8
Ek0-Ek1 > 0

Did you get my question? need a further explanation?
Integral
#5
Apr7-12, 04:31 PM
Mentor
Integral's Avatar
P: 7,321
Quote Quote by May11 View Post
Did you get my question? need a further explanation?
Sure does. This is simply not true in general. You need to tell about the system, and what it is doing. With the information given we can do nothing.
jtbell
#6
Apr7-12, 04:39 PM
Mentor
jtbell's Avatar
P: 11,787
Depending on the circumstances, an object's kinetic energy can either increase, decrease or remain constant. What are the circumstances in your case? What kind of object are we talking about? What forces act on it?
May11
#7
Apr7-12, 04:52 PM
P: 8
It is a plastic collision, masses exert forces on each other, ending up with a joint velocity (U). We fisrt have to express the equation of the velocity at the end of the collision, that is : U= Mv/M+m
Then, express the equation of Ek0 and Ek1 :
Ek0= Mv/2
Ek1= (m+M)u/2 = Mv/2(m+M)
Then, prove that Ek0-Ek1>0 ...that is pretty much all! we are not given any further...
May11
#8
Apr7-12, 04:53 PM
P: 8
Two masses, actually.
May11
#9
Apr7-12, 04:54 PM
P: 8
V1 (velocity of M before the collision) = v
V2 ( velocity of m before the collision) = 0
Nabeshin
#10
Apr7-12, 09:29 PM
Sci Advisor
Nabeshin's Avatar
P: 2,193
Quote Quote by May11 View Post
It is a plastic collision, masses exert forces on each other, ending up with a joint velocity (U). We fisrt have to express the equation of the velocity at the end of the collision, that is : U= Mv/M+m
Then, express the equation of Ek0 and Ek1 :
Ek0= Mv/2
Ek1= (m+M)u/2 = Mv/2(m+M)
Then, prove that Ek0-Ek1>0 ...that is pretty much all! we are not given any further...
Just write it out? It seems like you haven't even tried this.

[tex]E_0-E_1 = \frac{1}{2}Mv^2 - \frac{1}{2}\frac{M^2v^2}{m+M} = \frac{1}{2}Mv^2 \left( 1- \frac{M}{m+M} \right)[/tex]

Now what can you say about whether or not this is positive?
May11
#11
Apr8-12, 05:16 AM
P: 8
Mv/2 is undoubtedly positive.
1-M/m+M:
1>M/m+M
M+m>M<1 = positive.
Umm, makes sense. The teacher said we have to use more formulas which are not given in the question, haven't expressed them, to branch out a little from what we are given. I will ask if your proof is valid and acceptable.
Thanks a heap! :)
Nabeshin
#12
Apr8-12, 08:42 AM
Sci Advisor
Nabeshin's Avatar
P: 2,193
Quote Quote by May11 View Post
Umm, makes sense. The teacher said we have to use more formulas which are not given in the question, haven't expressed them, to branch out a little from what we are given. I will ask if your proof is valid and acceptable.
Thanks a heap! :)
Haha, that's an interesting stance to take. If you plan on continuing with physics, I suggest you try to get out of this mentality that there is a 'right' way of arriving at a solution. If a given derivation or proof seems logically sound to you, then it's good. I have some physics major friends who are in a similar mindset, and when doing problem sets with me they always say things like, 'can you do that?', as if there were some mystical physics police that sets the rules for how you approach physics problems! Of course there's not, and as long as you don't abuse math, everything's fine!

With re: to this problem, all the physics is essentially in solving for the final velocity (where you have to apply conservation of momentum).
May11
#13
Apr8-12, 03:02 PM
P: 8
I will bear that in mind !


Register to reply

Related Discussions
Can someone peek at a proof? (metric spaces, basic proof) Calculus & Beyond Homework 5
Did I skip a major step in this proof? + Theory of this proof Calculus & Beyond Homework 21
Proof Involving Continuity, Irrational Numbers From Elementary Proof Class Calculus & Beyond Homework 1
Comparison Proof via axioms, almost done need hints for finish and proof read Calculus & Beyond Homework 1
A proof is a proof-says Canadian Prime Minister General Math 0