Conservation of Energy and Momentum in an Explosion

In summary, the kinetic energy of the bomb pieces after explosion is the same whether they are moving or stationary.
  • #1
JamesG23
2
1
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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  • #2
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.
 
  • #3
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
 
  • #4
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.
 
  • #5
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!
 

FAQ: Conservation of Energy and Momentum in an Explosion

What is conservation of energy and momentum in an explosion?

Conservation of energy and momentum in an explosion is a fundamental principle in physics that states that the total energy and momentum of a system before and after an explosion must be equal. This means that the total energy and momentum cannot be created or destroyed, only transferred or transformed.

How does conservation of energy and momentum apply to explosions?

In an explosion, the initial potential energy of the explosive material is converted into kinetic energy as the material rapidly expands and moves outward. This increase in kinetic energy is balanced by a decrease in potential energy, and the total energy of the system remains constant. Similarly, the initial momentum of the explosive material is transferred to the surrounding objects, causing them to move in the opposite direction and maintaining the total momentum of the system.

What factors influence the conservation of energy and momentum in an explosion?

There are several factors that can affect the conservation of energy and momentum in an explosion. These include the type and amount of explosive material used, the surrounding environment and objects, and the direction and force of the explosion. Additionally, any external forces or factors, such as air resistance, can also impact the conservation of energy and momentum.

Are there any exceptions to conservation of energy and momentum in an explosion?

In most cases, conservation of energy and momentum holds true in explosions. However, there are some exceptions, such as nuclear explosions, where a small amount of mass is converted into energy according to Einstein's famous equation, E=mc². In these cases, the total energy of the system is still conserved, but the mass-energy equivalence principle must be taken into account.

Why is conservation of energy and momentum important in explosions?

Conservation of energy and momentum is important in explosions because it helps us understand and predict the behavior of explosive materials and their effects on the surrounding environment. By applying this principle, we can better design and control explosions for various purposes, such as mining, demolition, and propulsion. It also allows us to analyze and evaluate the potential dangers and risks associated with explosions.

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