Effective Area Ratio for Sky Diver's Terminal Speeds?

[mattmannmf]

The terminal speed of a sky diver is 170 km/h in the spread eagle position and is 305 km/h in the nose dive position.

a) Assuming the diver's drag coefficient C does not change from one position to the other, find the ratio of the effective cross section area in the slower position to that in the faster position.

I did 305/170= 1.794 but isn't the correct answer

 

[kuruman]

Hi mattmannmf, welcome to PF. Please use the homework template when you post homework related questions. What is the relevant equation that governs the terminal speed of the sky diver? What does the air-resistance depend on and how? Specifically, how does the terminal speed depend on the effective cross sectional area?

 

[mattmannmf]

i have no idea what anything you said means. that's all the problem gave me. i don't know anything else

 

[kuruman]

Is the problem at the end a textbook chapter? Is there a discussion in that chapter that explains the drag coefficient? How is the drag coefficient defined?

 

[mattmannmf]

right at the end of the chapter they talk about "drag forces" but they just say it depends on the objects area and speed...they leave no equations or anything. there's nothing in the summary page of that chapter saying anything about drag

 

[kuruman]

Does the object with the larger area have greater or smaller terminal velocity than the object with the smaller area. What do you think?

 

[mattmannmf]

the larger area has greater terminal velocity...terminal velocity is dependent on the surface area.

 

[kuruman]

The terminal speed of a sky diver is 170 km/h in the spread eagle position and is 305 km/h in the nose dive position.

Nose dive position has the greater terminal velocity. Does it also have the greater area? Picture the sky diver in your mind.

 

[mattmannmf]

No, area is smaller in the nose dive then in the spread out eagle position