Question about elastic/inelastic collision

[ryan9907]

The ball of mass 0.45kg hits the wall when it reaches maximum height of1.8m. The ball is incident witha horiziontal velocity of 6.6m/s and rebounds in a horizontal direction with a velocity of 5.2m/s. the ball is in contact with the wall for 0.22s.

State and explain whether the collision with the wall is elastic.

Answer given: Inelastic as speed is not conserved

My question: 1.do we assume that the wall speed is always 0? like the ball imparts a force on the wall, so there should be a net force acting on the wall and doesn't this mean the wall has acceleration and hence speed?
2. in this case, the answer said speed is not conserved so kinetic energy is not conserved, so what happened to the rest of the energy? converted to sound or heat?

3. If the ball hits with 6.6m/s and rebounds with 6.6m/s.. what does this mean? isit elastic?

This is just a Alevel question, thanks for your help

 

[Stonebridge]

This looks like it is part of a longer question, so it would be useful to see the rest. (The height and time of contact, for example, seem to have no purpose here). It's not quite clear exactly what this ball is doing prior to the collision.
However, what I can say is that the answer given is correct in that it is not an elastic collision. But I don't like the expression "speed is not conserved". I don't know of any "conservation of speed" principle in physics that applies here! (or anywhere)
It should be conservation of energy, and in particular, kinetic energy.
The kinetic energy after the collision is less than that before. This is, by definition, inelastic.
The energy will have been lost mostly as heat and sound.

 

[ryan9907]

Yes sir it's part of a longer qn about a ball on ground level being kicked onto the wall.

Nonetheless can u help me with Q1 and 3 :) thanks

 

[Doc Al]

My question: 1.do we assume that the wall speed is always 0? like the ball imparts a force on the wall, so there should be a net force acting on the wall and doesn't this mean the wall has acceleration and hence speed?

Yes, the ball imparts a force on the wall (which is presumably attached to some structure and the Earth itself) and thus the wall (and attached earth) will accelerate. But the mass of the wall+earth is so great that for all practical purposes the speed of the wall is zero.

3. If the ball hits with 6.6m/s and rebounds with 6.6m/s.. what does this mean? isit elastic?

Yes. Compare the initial and final KE.