, , , , , ,
-20, , . 65 150 /
3
7 : .
-
: " "
= 1,2 , h = 20 ., ρ= 13600 /3.
5. 9 ., , . 1 = 3*105 t1=-23C?, . t2=77
() , - ,
(7 ) .
7 :