The echo is weaker than the original sound since the echo has a smaller amplitude than the original sound because sound spreads and its intensity decreases with distance. For example, when the sound from a speaker is heard and is compared to its echo, the echo heard has a lower amplitude than the actual sound.
As a ball rolls ... even if there were no air resistance ... the ball
has to push down and climb over every one of those little fibers
that stick up from the felt fabric on the table. As it does that, each
little fiber brushes against the ball, and robs a tiny tiny bit of its
kinetic energy.
I think that numbers one, three, and four are true
You have to upload this in the area of mathematicians..!