Change the chapter
Question
(a) What is the rate of heat conduction through the 3.00-cm-thick fur of a large animal having a $1.40\textrm{ m}^2$ surface area? Assume that the animal’s skin temperature is $32.0^\circ\textrm{C}$ , that the air temperature is $-5.00^\circ\textrm{C}$ , and that fur has the same thermal conductivity as air. (b) What food intake will the animal need in one day to replace this heat transfer?
1. $39.7\textrm{ J/s}$
2. $820\textrm{ Calories}$
Solution Video

# OpenStax College Physics for AP® Courses Solution, Chapter 14, Problem 36 (Problems & Exercises) (2:15) Rating

No votes have been submitted yet.

Quiz Mode

Why is this button here? Quiz Mode is a chance to try solving the problem first on your own before viewing the solution. One of the following will probably happen:

1. You get the answer. Congratulations! It feels good! There might still be more to learn, and you might enjoy comparing your problem solving approach to the best practices demonstrated in the solution video.
2. You don't get the answer. This is OK! In fact it's awesome, despite the difficult feelings you might have about it. When you don't get the answer, your mind is ready for learning. Think about how much you really want the solution! Your mind will gobble it up when it sees it. Attempting the problem is like trying to assemble the pieces of a puzzle. If you don't get the answer, the gaps in the puzzle are questions that are ready and searching to be filled. This is an active process, where your mind is turned on - learning will happen!
If you wish to show the answer immediately without having to click "Reveal Answer", you may . Quiz Mode is disabled by default, but you can check the Enable Quiz Mode checkbox when editing your profile to re-enable it any time you want. College Physics Answers cares a lot about academic integrity. Quiz Mode is encouragement to use the solutions in a way that is most beneficial for your learning.

## Calculator Screenshots Video Transcript
This is College Physics Answers with Shaun Dychko. A fur covered animal is losing some heat to the environment through conduction and the animal's temperature is 32.0 degrees Celsius and the outside temperature is negative 5.00 degrees Celsius and in between the animal's skin, at this temperature, and the outside air, at this temperature, is some fur of thickness 3.00 centimeters which is 3.00 times 10 to the minus 2 meters and has a thermal conductivity equal to that of air which is 0.023 joules per second per meter per Celsius degree and the surface area of the animal we are told is 1.40 meters squared and the question in part (a) is what is the rate of heat transfer to the environment? So that's going to be the thermal conductivity multiplied by the surface area times the difference in temperature divided by the thickness of the animal's hair. So that's 0.023 times 1.40 meters squared times 32.0 minus negative 5.00 degrees Celsius divided by 3.00 times 10 to the minus 2 meters which is 39.7 joules per second. You could also write this with units of watts because watts is an abbreviation for joules per second. In part (b), we are asked how much food intake will the animal need in order to meet this energy requirement in order to replace this energy lost in a full day? So we multiply the rate at which energy is lost which is a power and then multiply that by the amount of time and we end up with 39.7133 joules per second multiplied by the number of seconds in a day so that's 24 hours times 3600 seconds per hour and these seconds cancel leaving us with joules and our answer is 3.4312 times 10 to the 6 joules. But food calories are usually written in this 'Calories' unit which is on the packages of the nutrition label for food and so we'll convert to food Calories by multiplying by 1 food Calorie for every 4186 joules. You could also think of this food Calorie as being a kilocalorie— those are the same thing. So 820 food Calories are needed to meet the energy needs of this heat loss.