Compression and rarefaction are two phenomenon occurs in longitudunal wave!
when there is denser particle gathering in that wave , there we called it compression and the rarer part of particles is rarefaction !
Wave speed (m/s) = frequency (Hz) x wave length (m)
=0.2 x 100= 20m/s
<span>Answer:
NASA in US using its super powerful telescope checks all the meteorites ,asteroids that may land on Earth. It deflects the asteroids ,meteorites from their respective path using copper ball . But it is not wholly practical as sometimes these meteorites get enter into key hole .</span>