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Interference
constructive interference
it scatters
it changes in velocity
speed
Interference
constructive interference
it scatters
it changes in velocity
speed
it blows up.
they annihilate each other
Reflection
Yes.
Nothing happens if you wave at them.
Nothing happens
It depends whether the new medium is "heavier" or "lighter" than the previous medium. If it is "heavier" then the wave slows down. If it is "lighter" the wave speeds up.