Originally posted by Miggi
A student wants to lose some weight. He knows that rigorous aerobic activity uses about 700 kcal/h (2900 kJ/h) and that it takes about 2000 kcal per day (8400 kJ) just to support necessary biological functions, including keeping the body warm. He decides to burn calories faster simply by sitting naked in a 16 C room and letting his body radiate calories away. His body has a surface area of about 1.7 m2 and his skin temperature is 35 C. Assuming an emissivity of 1.0, at what rate will this student "burn" calories? (kcal/h). If the student wants to lose 700kcal/day how much more time will this take him per day, compares to rigorous aerobic activity?
Finding rate at hich calories burn
T = 35 + 273 = 308 K
To = 16 + 273 = 289 K
P = e * sigma * A * (T^4 - To^4)
P = 1.0 x 5.67 x 10^-8 x 1.7 x (308^4 - 289^4)
P = 195 W
P = 195/4.14 cal/s = 47.1 cal/s
P = 47.1 * 10^-3 * 3600 kcal/h
P = 170 kcal/h (Answer)
Finding time taken
For the second part, are you sure it asks how much more
time? And is the value 700 kcal/day or 700 kcal/h ?