How to tell if energy was conserve in a momentum problem?

In summary, the two balls after impact will have different speeds due to the force of the collision. If the speed of the smaller ball before the collision is different from the speed of the smaller ball after the collision are not the same value then the kinetic energy is not constant, therefore it's energy is not conserved.
  • #1
Blockade
68
0
How can you determine if energy was conserve in a momentum problem? Let's say a small mass "m" hits a larger stationary mass "5m" where the smaller mass "m" flies bounces upward and the larger mass "5m" bounces in a negative downward direction.

So from them bouncing off each other I know that it's an elastic type of collision. What I also know is that the initial velocity of both masses are not the same after impact.

Can any of these clues allow me to tell if energy was conserve within the system?

Note: The picture is just something I made up and the values of the different velocities just demonstrate that the smaller ball loses speed after impact.

Does that mean that energy is not conserved since the smaller ball losses speed and therefore it losses kinetic energy? Does this make it an elastic collision instead of a perfectly elastic one?

4a89d4ae6b.png
 
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  • #2
No, you cannot tell from the information you present.
If you know both velocities before and after collision, of course you can check if the KE is conserved.
If not, you need to know something about the materials. The quantity that tells "how ellastic" is the collision is called restitution coefficient. You can gind it for various pairs of materials.
 
  • #3
nasu said:
No, you cannot tell from the information you present.
If you know both velocities before and after collision, of course you can check if the KE is conserved.
If not, you need to know something about the materials. The quantity that tells "how ellastic" is the collision is called restitution coefficient. You can gind it for various pairs of materials.

So if energy is conserved then the speed before impact should equal the speed after impact?
 
  • #4
No, not at all. Where did you get this from? And what speed are you talking about? There are two speeds after a two-body collision.
And two speeds before collision. What would you mean by "the speed after impact should equal the speed after impact"?
 
  • #5
nasu said:
No, not at all. Where did you get this from? And what speed are you talking about? There are two speeds after a two-body collision.
And two speeds before collision. What would you mean by "the speed after impact should equal the speed after impact"?

I mean the speed of the smaller ball (red). I thought that if the speed of the smaller ball before the impacted is different from the speed of the smaller ball after the impact are not the same value then the kinetic energy is not constant, therefore it's energy is not conserved. I think that my reasoning and definitions are wrong then.
 

FAQ: How to tell if energy was conserve in a momentum problem?

1. How do you determine if energy was conserved in a momentum problem?

The conservation of energy in a momentum problem can be determined by comparing the total initial energy (kinetic and potential) to the total final energy. If the two are equal, then energy was conserved.

2. What is the equation for calculating energy in a momentum problem?

The equation for calculating energy in a momentum problem is E = 1/2 mv^2 + mgh, where m is the mass, v is the velocity, g is the acceleration due to gravity, and h is the height.

3. Can energy be lost or gained in a momentum problem?

Yes, energy can be lost or gained in a momentum problem. This can happen if there are external forces acting on the system, such as friction or air resistance, which can change the amount of kinetic or potential energy present in the system.

4. How does the conservation of energy relate to the conservation of momentum?

The conservation of energy and the conservation of momentum are related because they both involve the idea that energy and momentum cannot be created or destroyed, but can only be transferred or converted into different forms.

5. What are some real-life examples of energy conservation in momentum problems?

Some real-life examples of energy conservation in momentum problems include a pendulum swinging back and forth, a ball rolling down a ramp, or a rocket launching into space. In all of these situations, the initial energy is converted into kinetic energy, and then back into potential energy, demonstrating the conservation of energy.

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