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MJC8719
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An explosion breaks an object into two pieces, one of which has 1.60 times the mass of the other. If 7100 J were released in the explosion, how much kinetic energy did each piece acquire?
Heavier Piece
Lighter Piece
Express KE in terms of P
I think I have done most of the work here...its the last part of the problem that's tripping me up
Heres my work:
The explosion causes the piece (which I'm assuming explodes while at rest) to break into two pieces. Conservation of momentum states that they must go in opposite directions (you can verify this on your own). So, we have our first equation:
mv1 + 1.6mv2 = 0
mv1 = -1.6mv2
v2 = -v1/1.6
I use v1 for the velocity of the lighter piece, and v2 for the heavier piece. The energy of the explosion is transferred to the pieces and causes it to move, so the sum of the kinetic energies of the two pieces combined must equal 7100 J. Our second equation is:
1/2mv12 + 1/2 (1.6m)v22 = 7100
If we substitute v2 with what we got before with momentum conservation, then we can get the left hand side to be in terms of m and v1 only. We can't find the values of m and v1 directly, but we know that the kinetic energy (of the lighter piece) is 1/2mv12, which we can find after rearranging the equation so that it is in the form of kinetic energy:
1/2mv12 + 1/2(1.6m)(-v1/1.6)2 = 7100 J
1/2m(v12+v12/1.6) = 7100 J
1/2m(1.625v12) = 7100 J
1/2mv12 = 4370 J
Now here's where it starts to get a little tricky:
The final line reads: 1/2 mv1^2 = 4370.
So, we also then know that K = 1/2mv^2 = (1/2)(m^2v^2/m) = p^2/2m
Therefore, p^2/2m = 4370
So, the energy for lighter piece would then equal 4370 - p^2/2m and thus the energy for the heavier piece would just be 1- that.
Is this correct? I am slighty confused by the fact that my answer has to be in terms of P.
Thanks for the help
Heavier Piece
Lighter Piece
Express KE in terms of P
I think I have done most of the work here...its the last part of the problem that's tripping me up
Heres my work:
The explosion causes the piece (which I'm assuming explodes while at rest) to break into two pieces. Conservation of momentum states that they must go in opposite directions (you can verify this on your own). So, we have our first equation:
mv1 + 1.6mv2 = 0
mv1 = -1.6mv2
v2 = -v1/1.6
I use v1 for the velocity of the lighter piece, and v2 for the heavier piece. The energy of the explosion is transferred to the pieces and causes it to move, so the sum of the kinetic energies of the two pieces combined must equal 7100 J. Our second equation is:
1/2mv12 + 1/2 (1.6m)v22 = 7100
If we substitute v2 with what we got before with momentum conservation, then we can get the left hand side to be in terms of m and v1 only. We can't find the values of m and v1 directly, but we know that the kinetic energy (of the lighter piece) is 1/2mv12, which we can find after rearranging the equation so that it is in the form of kinetic energy:
1/2mv12 + 1/2(1.6m)(-v1/1.6)2 = 7100 J
1/2m(v12+v12/1.6) = 7100 J
1/2m(1.625v12) = 7100 J
1/2mv12 = 4370 J
Now here's where it starts to get a little tricky:
The final line reads: 1/2 mv1^2 = 4370.
So, we also then know that K = 1/2mv^2 = (1/2)(m^2v^2/m) = p^2/2m
Therefore, p^2/2m = 4370
So, the energy for lighter piece would then equal 4370 - p^2/2m and thus the energy for the heavier piece would just be 1- that.
Is this correct? I am slighty confused by the fact that my answer has to be in terms of P.
Thanks for the help