Exploring Inelastic Collisions: Energy Conservation

[Misr]

hi,
Look at this experiment
http://img243.imageshack.us/img243/4150/inelasticcollision2.jpg

http://img13.imageshack.us/img13/2914/inelastic2.jpg

in this experiment , the law of conservation of energy can't be applied because the KE is lost
but this is not true for all the cases of inelastic collision.
for example
when the ball hits the ground , we hear a sound and if the ball rebounded it doesn't reach the same height because KE is converted into sound energy but not lost so law of conservation of energy can be applied although its inelastic collision.

so why the book wrote that "in elastic collision the law of conservation of energy can't be applied"
although this doesn't work at all cases (i think so)

 

[Stonebridge]

It's just a case of careless wording in the book.
It should say that conservation of mechanical (in this case k.e. and p.e.) energy cannot be applied. The broader application of conservation of energy, where you include other forms such as sound, always applies.
In many books, when dealing with mechanics problems like this one, "energy" is taken to mean mechanical energy.

 

[Misr]

Yes , thank you