Elastic and inelstic collisions conceptual questions.

In summary, the questions asked the respondent if the collisions in the drawings could be elastic or inelastic. The respondent was not given any information about the mass of the particles, angles, or velocity. However, the respondent was given the direction and magnitude of the collision, and the dot representing the collision. The respondent attempted to solve the problem by thinking about elastic collisions and reversing the arrows. conservation of energy states that the process is in principle reversible, and that what remains to check is whether there is a change in entropy.
  • #1
R_moor
10
0

Homework Statement


The questions showed in the pictures ask me whether the collisions in the drawings could be elastic or inelastic, I am not given any mass, the angles are a little vague but I think B and C are supposed to be π/2 and π respectively. For velocity, I am just given the direction and somewhat the magnitude but no numbers. Also the dot represents where the particles collided.

Homework Equations


Conservation of momentum: P_initial = P_final
Conservation of energy: KE initial = KE energy final + Q
Q is just the energy lost or gained during the collision.

The Attempt at a Solution


So far I think that all of them could be elastic and inelastic as without any information of the initial state of the system I can't know whether we are loosing some kinetic energy or not. The problem is I'm not sure whether my reasoning is correct as I am not sure how can I prove this. Any help to reason out the correct answer would be very appreciated.
 

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  • #2
There is a very easy way to think about 1d: "backwards".
 
  • #3
1f is somewhat problematic. A collision is inelastic if any KE is lost, no matter how little. Consequently, if a diagram depicts an elastic collision, the same diagram could work for inelastic, however slightly.
My guess is that for 1f you are supposed to consider whether it could have been "perfectly inelastic". That means, as much KE was lost as is consistent with conservation of momentum, no friction, point masses (so no rotation) and non-penetration (they cannot pass through each other).
 
  • #4
haruspex said:
There is a very easy way to think about 1d: "backwards".
Sorry I'm not sure what you mean by working it backwards. Could you explain a little more please
 
  • #5
R_moor said:
Sorry I'm not sure what you mean by working it backwards. Could you explain a little more please
A feature of elastic collisions is no change in entropy. The process is in principle reversible, i.e., you can run time backwards to recreate the initial condition. Just reverse the arrows. What does it remain to check?
 
  • #6
haruspex said:
A feature of elastic collisions is no change in entropy. The process is in principle reversible, i.e., you can run time backwards to recreate the initial condition. Just reverse the arrows. What does it remain to check?
Sorry for late reply, Thanks for the help !
 
  • #7
R_moor said:
Sorry for late reply, Thanks for the help !
Does this mean you have answered the question?
Were you able to answer my question at the end of post #5?
 

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

Elastic collisions are those in which both kinetic energy and momentum are conserved, meaning the total energy and total momentum of the system remain constant before and after the collision. Inelastic collisions, on the other hand, involve a loss of kinetic energy due to the conversion of kinetic energy into other forms such as heat or sound.

2. How do you determine if a collision is elastic or inelastic?

The coefficient of restitution (e) is used to determine whether a collision is elastic or inelastic. An e value of 1 indicates a perfectly elastic collision, while an e value of 0 indicates a completely inelastic collision. Any value between 0 and 1 represents a partially elastic collision.

3. Can a collision be both elastic and inelastic?

No, a collision cannot be both elastic and inelastic. It is either one or the other, depending on the amount of kinetic energy lost during the collision.

4. How does the mass of the objects involved in a collision affect its elasticity?

The mass of the objects involved in a collision does not affect its elasticity. Elasticity is determined by the coefficient of restitution, which depends on the nature and properties of the objects involved, not their masses.

5. Is momentum conserved in both elastic and inelastic collisions?

Yes, momentum is always conserved in both elastic and inelastic collisions. In elastic collisions, both momentum and kinetic energy are conserved, while in inelastic collisions, only momentum is conserved.

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