Kinetic Energy Problem

  • Thread starter Bones
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  • #1
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Homework Statement



An internal explosion breaks an object, initially at rest, into two pieces, one of which has 1.6 times the mass of the other. If 25000 J is released in the explosion, how much kinetic energy does each piece acquire?

Homework Equations





The Attempt at a Solution


I am not sure where to begin.
 

Answers and Replies

  • #2
LowlyPion
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Homework Statement



An internal explosion breaks an object, initially at rest, into two pieces, one of which has 1.6 times the mass of the other. If 25000 J is released in the explosion, how much kinetic energy does each piece acquire?

Homework Equations



The Attempt at a Solution


I am not sure where to begin.

Here is a similar problem:
https://www.physicsforums.com/showthread.php?t=267683
 
  • #3
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Ok so m1=1.6m2
How do I figure out v1?
 
Last edited:
  • #4
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Would v1 be 1/1.6v2?
 
  • #5
LowlyPion
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Would v1 be 1/1.6v2?

It depends on which piece is the heavier.

What must be true in this problem?
 
  • #6
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The heavier piece will have less velocity than the lighter piece.
 
  • #7
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25000 J = 2.6/1.6 * 1/2 * m2v22
So 25000J*.81=20250J for the lighter piece and 25000J-20250J=4750J for the heavier piece.
Is that correct??
 
  • #8
LowlyPion
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25000 J = 2.6/1.6 * 1/2 * m2v22
So 25000J*.81=20250J for the lighter piece and 25000J-20250J=4750J for the heavier piece.
Is that correct??

Not quite.

They want the KE of the pieces. And the KE is mv2/2 not mv2

Check your math.
 
  • #9
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I am not sure what I am doing...that was just kinda of a guess.
 
Last edited:
  • #10
LowlyPion
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I am not sure what I am doing...that was just kinda of a guess.

25000 J = 2.6/1.6 * 1/2 * m2v22

So what does mv2/2 equal in your equation?

Isn't that the KE of m2?

Isn't that 1 part of what they asked?
 
  • #11
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So 25000 J=2.6/1.6*1/2mv2v2^2 which is the same thing as 25000 J=2.6/1.6*mv2v2^2/2

25000J=0.8125m2v2

Am I on the right track?
 
Last edited:
  • #12
LowlyPion
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So 25000 J=2.6/1.6*1/2mv2v2^2 which is the same thing as 25000 J=2.6/1.6*mv2v2^2/2

Yes but 25000 J = 2.6/1.6 * 1/2*m*v2 = 2.6/1.6 * KE2

Isn't the question "Find KE1 and KE2" ?
 
  • #13
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Yes.
So 1.625*KE2=25000
KE2=15385J the lighter piece
KE1=9615J the heavier piece
?
 
  • #14
LowlyPion
Homework Helper
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Yes.
So 1.625*KE2=25000
KE2=15385J the lighter piece
KE1=9615J the heavier piece
?

That's what it looks like.
 
  • #15
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Great! Thanks ;)
 

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