Conservation of momentum elastic and inelastic collisions

[Richard Feynman 101]

Question: an object weight m Kg is travelling at V ms-1 and collides with a stationary object that does not move. Is this an elastic or an inelastic collision? And if so, where does the energy of the object go? (hint - energy is not always kinetic and gravitational potential energy).

A harder question is: if friction is negligible are stationary objects that are involved in collisions always elastic?

[Cassidyhogi]

For the first question:
This is an inelastic collision since the initial kinetic energy is more than the final kinetic energy (kinetic energy equals 0.5mv^2)
The rest of the energy may transform into thermal energy as a result of the friction on the moving object, and also sound energy as the objects collide.

For the harder question: I think if friction is negligible there are still other forms of energy that kinetic energy can be transformed into other than thermal, such as sound as I mentioned above. Hmm, can't really think of another type sorry.

[Richard Feynman 101]

For the first question:
This is an inelastic collision since the initial kinetic energy is more than the final kinetic energy (kinetic energy equals 0.5mv^2)
The rest of the energy may transform into thermal energy as a result of the friction on the moving object, and also sound energy as the objects collide.

For the harder question: I think if friction is negligible there are still other forms of energy that kinetic energy can be transformed into other than thermal, such as sound as I mentioned above. Hmm, can't really think of another type sorry.

Yep. First one is correct. The second one - mmm, not so. You see when you drop a ball from say 5 meters high and it haves 50 Joules of energy and it does not bounce back at all is a completly inelastic collision, but we did that 50 Joules of energy go - well, it actually becomes internal energy in the ball and the floor itself that collided.

[Yertle the Turtle]

For the first question, when you say that the stationary object does not move, you do not mention if the original object moves at all. In general, this would be an inelastic collision, since the kinetic energy is lost in sound and heat.

For the second question, the sound produced will stop this being an elastic collision. If you think in terms of billiard balls, the balls will slow down due to the friction on the table, but there is a small amount of sound as they collide. This is what will always make this an inelastic collision.

In the case of your last point, the 50J energy has gone to sound, and also into the ball and the ground as you say, but there is almost always some bounce back. The movement of the particles to absorb the energy, and the sound produced will rarely take up the whole energy, but as a whole, your statement is correct, I believe. ;P