Elastic or inelastic collision?

In summary: Yes, the typical assumption with "stick together" is a head-on collision, ignoring the possibility of a resulting rotation. But a literal reading of the problem statement in #1 above allows the possibility.
  • #1
Mohamad
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1
If the initial kinetic energy is equal to the final kinetic energy where two objects that collide stick together, this collision is elastic or inelastic?
 
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  • #2
If my grandmother has wheels she still isn't a school bus.
What collision scenario do you have in mind ?
 
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  • #3
Mohamad said:
Summary: elastic or inelastic collision?

If the initial kinetic energy is equal to the final kinetic energy where two objects that collide stick together, this collision is elastic or inelastic?
Clearly you do not understand the basic definitions of elastic and inelastic collision. You could at least look those up before proceeding.
 
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  • #4
An "elastic collision" is, by definition, one in which kinetic energy is conserved. Since, in an inelastic collision, we don't have the "conservation of kinetic energy" equation, we need another condition to solve for the speeds after the collision. Often that is given by requiring that the two objects stick together, but that is not necessary. We can have an inelastic collision in which the two objects do not stick together and we can have an elastic collision in which the two objects do stick together. Here, we are given that kinetic energy is conserved so this has to be an elastic collision.
 
  • #5
HallsofIvy said:
An "elastic collision" is, by definition, one in which kinetic energy is conserved. Since, in an inelastic collision, we don't have the "conservation of kinetic energy" equation, we need another condition to solve for the speeds after the collision. Often that is given by requiring that the two objects stick together, but that is not necessary. We can have an inelastic collision in which the two objects do not stick together and we can have an elastic collision in which the two objects do stick together. Here, we are given that kinetic energy is conserved so this has to be an elastic collision.
I thought we weren't supposed to spoon-feed the answers. :frown:
I had already asked him to look up the defintions so that he could figure that out for himself.
 
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  • #6
Using conservation of momentum (which holds regardless if the collision is elastic or inelastic,unless there is net external force which is comparable in magnitude with the magnitude of the big forces that arise due to collision) we can prove that IF the two bodies stick together then the kinetic energy isn't conserved.

So your scenario is contradictory. Either the bodies don't stick together, or the kinetic energy isn't conserved, you can't have both. OR there are external forces in play.
 
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  • #7
Delta2 said:
So your scenario is contradictory. Either the bodies don't stick together, or the kinetic energy isn't conserved, you can't have both. OR there are external forces in play.
Or the objects were spinning just right so that they could latch onto one another without dissipating any energy. They can then spin about one another, each retaining its original (and rotational) kinetic energy in the combined center-of-momentum frame.
 
  • #8
jbriggs444 said:
Or the objects were spinning just right so that they could latch onto one another without dissipating any energy. They can then spin about one another, each retaining its original (and rotational) kinetic energy in the combined center-of-momentum frame.
The way I interpreted "stick together" is that they have exactly the same velocity after the collision. In the scenario you describe they don't have the same velocity after the collision (spinning about one another means they have opposite and equal velocities (in the best scenario) if I understand it properly)
 
  • #9
Delta2 said:
The way I interpreted "stick together" is that they have exactly the same velocity after the collision. In the scenario you describe they don't have the same velocity after the collision (spinning about one another means they have opposite and equal velocities (in the best scenario) if I understand it properly)
Yes, the typical assumption with "stick together" is a head-on collision, ignoring the possibility of a resulting rotation. But a literal reading of the problem statement in #1 above allows the possibility.
 

1. What is the difference between elastic and inelastic collision?

Elastic collision is a type of collision where the total kinetic energy of the system is conserved, meaning that the objects involved bounce off each other without any loss of energy. In contrast, inelastic collision is a type of collision where some of the kinetic energy is lost to other forms of energy, such as heat or sound.

2. How does momentum play a role in elastic and inelastic collisions?

Momentum, which is the product of an object's mass and velocity, is conserved in both elastic and inelastic collisions. However, in elastic collisions, the objects involved have the same velocity before and after the collision, while in inelastic collisions, the objects have different velocities after the collision due to the loss of kinetic energy.

3. Can you provide an example of an elastic and an inelastic collision?

An example of an elastic collision is when two billiard balls collide on a pool table. The total kinetic energy of the system remains the same before and after the collision, and the balls bounce off each other without any loss of energy. An example of an inelastic collision is when a car collides with a wall. Some of the car's kinetic energy is converted into other forms of energy, such as heat and sound, upon impact with the wall.

4. How do you calculate the coefficient of restitution in elastic and inelastic collisions?

The coefficient of restitution is a measure of the elasticity of a collision and is calculated by dividing the relative velocity of the objects after the collision by the relative velocity before the collision. In elastic collisions, the coefficient of restitution is equal to 1, while in inelastic collisions, it is less than 1.

5. What real-world applications involve elastic and inelastic collisions?

Elastic and inelastic collisions have various real-world applications, such as in sports, transportation, and engineering. For example, the principles of elastic and inelastic collisions are used in designing airbags for cars, in the construction of bumper cars, and in the development of safety equipment for athletes. In addition, understanding these types of collisions is crucial in industries such as aerospace and manufacturing, where the impact of objects is a common occurrence.

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