# PHYSICS

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If Superman is flying at mach 4, 1 km above the ground and yells "Hey! Finish your test!" from directly overhead, what does it sound like when you finally hear him? Superman travels slower than light and therefore you don't hear him until he is 4.1231 kilometers away.
Speed of Sound = 340 m/s

How do I even answer this?

• PHYSICS - ,

I am uncertain of the question. The time it took for the sound to travel 1km is the time it took a mach4 plane to travel 4.1231km.

so, time to travel 1km=340m/s*t or t= 1/340 sec

velocity of superman= 4.1231km/(1/.340)=4.1231*.340 km/s=1.40km/s which in fact is about mach4.
So I don't know the question.

• PHYSICS - ,

The question was what does it sound like when you hear his sentence?
But I have no idea how to answer it.

• PHYSICS - ,

It sounds like "Hey! Finish your test!"
because when he made the noise he was not moving toward or away from you. He was directly over head and had at that instant no velocity component toward or away from you. Therefore no Doppler effect.

• PHYSICS - ,

Oh! Okay thank you so so so much guys! :)