# Fat: the fuel of migrating birds

1. Sep 25, 2007

[SOLVED] Fat: the fuel of migrating birds

Consider a bird that flies at an average speed of 10.7 m/s and releases energy from its body fat reserves at an average rate of 3.70 W (this rate represents the power consumption of the bird). Assume that the bird consumes 4g of fat to fly over a distance d without stopping for feeding. How far will the bird fly before feeding again?

First of all, this is an extremely weird question. And as always i find myself stuck. Anyone can give me a hint as to how i would approach this thing???
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i know power = change in work / change in time = 3.7 ... and that work = FDcos(theta)

2. Sep 25, 2007

### mgb_phys

There must be part of the question missing.
You need to know the mass of the bird and the ratio of fat, otherwise you could have an albatross with 10kg of fat or a hummingbird with 0.1g.

3. Sep 26, 2007

No. I think I gave everything...

Unless you want to know this short blurb as well: Small birds can migrate over long distances without feeding, storing energy mostly as fat rather than carbohydrate. View Figure Fat is a good form of energy storage because it provides the most energy per unit mass: 1 gram of fat provides about 9.4 (food) Calories, compared to 4.2 (food) Calories per 1 gram of carbohydrate. Remember that Calories associated with food, which are always capitalized, are not exactly the same as calories used in physics or chemistry, even though they have the same name. More specifically, one food Calorie is equal to 1000 calories of mechanical work or 4186 joules. Therefore, in this problem use the conversion factor 1 Cal = 4186 J.

4. Sep 26, 2007

### mgb_phys

It's still not enough 10.7m/s and 3.7J/s tells you that it takes 2.9J to fly each m.
You can work out how many J are in 4g of fat and how far you can fly on that, but to know how far the bird can fly you need the total amount of fat it has onboard.

5. Sep 26, 2007

yeah i worked it out and got the right ans. thanks for everything ..

6. Sep 26, 2007

### mgb_phys

So the question assumed that the 4g of fat were all the bird had? It doesn't say that.

7. Sep 26, 2007

the question was just how far can the bird fly on that 4 g of fat, i guess..

8. Oct 28, 2007

### Tee07

I'm having issues with this question as well. From what you guys have posted so far.. i just figured out the distance to be ~54 km? (which is wrong) Can someone clarify how to work this one out?

I've found that 4g fat = 37.6 Cal = 157 393.6 J

So,

(157 393.6J) (1m/2.89J) = 54 461.5m = ~54 km ...

9. Nov 14, 2007

### greentea987

Please help me with this problem! I have no idea how to get the answer and the assignment is due tomorrow, can anyone just walk me through the steps and help me out?

10. Nov 14, 2007

### greentea987

Could you please explain to me what you did for the problem? I really do not understand it and my teacher won't help me out with it. All I need is a quick explanation, please!

11. Nov 14, 2007

### Supernats

Find the amount of energy in 4g of fat, then use power to find out how long it will last. Then it should be pretty clear.

12. Nov 14, 2007

### greentea987

Thank you thank you!

13. Nov 14, 2007

### greentea987

I still don't understand, how would you go about finding the amount of energy and how do you calculate power and from there how do I use power to figure out how long it lasts?