Why Is Total Kinetic Energy Conserved in Some Collisions but Not in Others?

[jack1234]

For this question
http://tinyurl.com/2btmot
the solution for question 6(c) is assume conservation of energy(total kinetic energy before collision = total kinetic energy after collision)

I am very confused here.

May I know why sometimes when two body collides, the total kinetic energy before collision is not equal to the total kinetic energy after the collision(although their momentum is equal)? Where are the kinetic energy goes?

For this question, what make us think that this is an elastic collision?

 

[muppet]

Energy is always conserved, as you know. However, it doesn't have to stay in the same form; it's sometimes dissipated from a system. Replace your airtrack with sandpaperand you'd quickly conclude that friction would be massive, so loads of energy would be wasted overcoming that. If the spring wasn't there, the gliders would crack together, and energy would be lost as sound; my old school used magnets instead to achieve the same effect.
In general, think about where energy can be lost from your system. If the question includes features that minimise those losses (the classic keyword is "smooth surface") then you're being encouraged to assume an elastic collision.

 

[ogb p]

It is important to understand that there are different types of collisions, and each type has its own set of rules and principles. In an elastic collision, the total kinetic energy before and after the collision remains the same. This means that the energy is conserved and no energy is lost during the collision. In contrast, in an inelastic collision, some of the kinetic energy is converted into other forms of energy, such as heat or sound, and the total kinetic energy after the collision is less than before.

In the case of an elastic collision, the assumption of conservation of energy is made because it is a fundamental principle in physics. This means that energy cannot be created or destroyed, only transferred from one form to another. So, in an elastic collision, the total kinetic energy before the collision is equal to the total kinetic energy after the collision because no energy is lost or gained.

As for why sometimes the total kinetic energy before and after a collision may not be equal, it depends on the type of collision and the objects involved. In a perfectly elastic collision, the objects involved must be perfectly rigid and there can be no external forces acting on them. In real-world scenarios, this is not always the case, and there may be factors such as friction or deformation that can affect the total kinetic energy.

In conclusion, the assumption of conservation of energy in an elastic collision is based on the fundamental principle that energy is conserved. This means that in an ideal elastic collision, the total kinetic energy before and after the collision will be the same. However, in real-world situations, this may not always hold true due to external factors. It is important to consider all the variables and principles involved when analyzing a collision and determining whether it is elastic or not.