KE Loss Qs 8: Elastic Collisions Explained

[yolo123]

8. All KE is lost when:
(a) two bodies of equal mass collide,
(b) two bodies of opposite initial velocity collide,
(c) two bodies of equal mass and opposite initial velocity collide,
(d) never.

None of these make sense to me.
(a) Billard balls have elastic collisions.
(b) Billard balls again disprove this...
(c) Billard balls...
(d) ...... Elastic collisions exist.

 

[zeralda21]

Kinetic energy is lost in inelastic collisions. Does that help? Total energy is however conserved.

 

[yolo123]

Yes. I don't see how that helps though. My counter-examples still hold true.

 

[guitarphysics]

Your 'counterexample' on part (d) is incorrect; so what if elastic collisions exist? That tells us nothing about a case where *all* KE is lost, which is what the question is about.

As for the question itself, I'm not actually sure! . Are you completely sure it was "All KE is lost when" and not "All KE *can* be lost when"? That would make more sense, because in all the examples it can be conserved as well, depending on whether the collision is elastic or not. Or maybe I'm just delirious because it's midnight. Oh well.

 

[HalfLostAndSearching]

I can provide a response to this content by explaining the concept of elastic collisions and addressing each of the given scenarios.

Elastic collisions are collisions between two objects where the total kinetic energy (KE) of the system is conserved. This means that the sum of the KE of the two objects before the collision is equal to the sum of the KE after the collision. In other words, no KE is lost during an elastic collision.

(a) In the scenario of two bodies of equal mass colliding, the total KE of the system would not be lost, as it is conserved in an elastic collision. However, the KE of each individual body may change depending on the direction and speed of their motion after the collision.

(b) When two bodies of opposite initial velocity collide, the total KE of the system would still be conserved in an elastic collision. This is because the KE of one body would decrease while the KE of the other would increase, resulting in a balanced exchange of energy.

(c) Similarly, in the scenario of two bodies of equal mass and opposite initial velocity colliding, the total KE of the system would still be conserved. The KE of one body would decrease, while the KE of the other would increase, resulting in the same balanced exchange of energy.

(d) It is incorrect to say that all KE is lost in elastic collisions. In fact, elastic collisions are defined by the conservation of KE. This means that in any scenario, as long as the collision is elastic, no KE is lost.

In conclusion, elastic collisions do exist and they are characterized by the conservation of KE. It is important to understand the concept of elastic collisions in order to accurately analyze and predict the behavior of objects in motion. The example of billiard balls is often used to demonstrate the concept of elastic collisions, as they are designed to have minimal energy loss during collisions.