SUPPOSE THAT ON A COLD WINTER DAY ( T, = 7 C), YOU QUICKLY LEAVE YOUR HOUSE DRESSED ONLY IN A 0.3 cm THICK COTTON SHIRT, WHICH THERMAL CONDUCTIVITY IS (K, = .2 BTU/h -m- c ). HOW LONG WILL IT TAKE FOR YOU TO ENTER HYPOTHERMIA IF YOU STAY OUTDOORS? (YOUR BODY TEMPERATURE IS Tc-37C, AND HYPOTHERMIA OCCURS AT 27C).

ASSUME THAT YOU ONLY LOSE HEAT THROUGH YOUR CHEST AND BACK (CONSIDER YOUR THORAX AS A RECTANGULAR BLOCK, AND MEASURE IT TO KNOW ITS AREA [length x width], LET'S ALL TAKE 0.36 m); THE WALL OF YOUR BODY IS SKIN WITH GREASE WITH A THICKNESS OF 2 cm., WHOSE THERMAL CONDUCTIVITY IS K = .18 BTU/ h- m-c, AND THE HEAT TRANSFER COEFFICIENT OF YOUR BODY WITH THE ENVIRONMENT IS: h, 4 BTU / h-m -c.

ALSO, HOW LONG WILL IT TAKE FOR YOU TO GET HYPOTHERMIA, IF YOU THEN COVER YOUR BODY WITH

a).- A 0.5 cm THICK DENIM JACKET

(K-1.5 BTU/h-m-c)

b).- A LEATHER JACKET 0.5 cm THICK (Kr-2.2 BTU/h-m-c)

c).-A 2 cm THICK GOOSE DOWN JACKET (Kec.-0.034 BTU/h-m-"c)

d) WHY DO YOU BELIEVE OLETS TA