Conservation of Energy and Momentum in an Explosion

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SUMMARY

The discussion focuses on the conservation of energy and momentum during an explosion, specifically analyzing kinetic energy (KE) before and after the event. The calculations presented indicate that the total KE of bomb pieces after the explosion is 130 J, while the KE before detonation was 90 J. The conclusion drawn is that the original KE is conserved, as the difference in KE before and after the explosion equals the KE of the bomb pieces when stationary, which is 40 J. This illustrates that the energy is not lost but rather redistributed in the explosion process.

PREREQUISITES
  • Understanding of kinetic energy calculations (1/2mv²)
  • Familiarity with the concepts of conservation of momentum and energy
  • Basic knowledge of physics related to explosions and gas dynamics
  • Ability to analyze and interpret lab frame observations in physics
NEXT STEPS
  • Study the principles of conservation of momentum in explosive events
  • Learn about the effects of atmospheric pressure on explosion dynamics
  • Explore advanced kinetic energy calculations in multi-body systems
  • Investigate the physics of gas expansion and its impact on energy distribution
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Physics students, educators, and professionals interested in the mechanics of explosions, energy conservation, and momentum analysis in dynamic systems.

JamesG23
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Hey, I have a question about explosions and how kinetic energy works during them. I have outlined my question on the attached image. Please let me know if something is wrong or needs clarifying. Thank you.

IMG_2061.png
 
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It would be easier to comment if you had typed up your work. But anyway:

Viewed from the lab frame, you calculated the total KE after the explosion = (26m)/4. Sounds good. Not sure why you set that equal to 4m.

The KE before explosion = (1/2)m(9) = (18m)/4. Subtract that from the KE after the explosion and see what you get.
 
Doc Al said:
It would be easier to comment if you had typed up your work. But anyway:

Viewed from the lab frame, you calculated the total KE after the explosion = (26m)/4. Sounds good. Not sure why you set that equal to 4m.

The KE before explosion = (1/2)m(9) = (18m)/4. Subtract that from the KE after the explosion and see what you get.
Oh shoot I don't know why I simplified like that. Maybe I thought it was 24/6. Thank you
 
JamesG23 said:
I have a question about explosions and how kinetic energy works during them.
In an atmosphere, the explosion of a flying bomb produces a sphere of hot combustion gas that has a very low density compared to the original explosive charge.
That sphere is effectively stopped immediately by it's low mass and the area of it's greater cross-section.
The original KE is not lost, it is just insignificant when applied to the huge mass of atmosphere that encloses the explosion.
 
Let's say the bomb pieces are 10kg each.
KE of each piece at ±2 m/s: 1/2mv2=20J
Total KE of bomb pieces: 40 J

KE of both bomb pieces at +3 m/s before detonation: 90 J
KE of bomb piece at +5m/s: 125 J
KE of bomb piece at +1 m/s: 5 J
Total KE of bomb pieces after explosion: 130 J

But look. 125+5-90 = 40 J
The same as when the bomb is stationary!
 

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