Asked by Anonymous
                 boy throws a penny into an empty well with an initial velocity of –2 m/s. He hears it hit the bottom 8 seconds later. About how far did the penny fall?
            
            
        Answers
                    Answered by
            bobpursley
            
    t'=time to fall
t"=time for sound to return after bottom
t'+t"=8
depth=2*t'+1/2 g t'^2
depth=velocitysound*t"
set them equal (same depth)
2*t'+1/2 g t'^2=velocitysound*t"
2*t'+1/2 g t'^2=velocitysound*(8-t')
so solve for t', and then you can get depth.
    
t"=time for sound to return after bottom
t'+t"=8
depth=2*t'+1/2 g t'^2
depth=velocitysound*t"
set them equal (same depth)
2*t'+1/2 g t'^2=velocitysound*t"
2*t'+1/2 g t'^2=velocitysound*(8-t')
so solve for t', and then you can get depth.
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