Question about terminal speed using drag

[sona1177]

What is the terminal speed of a 75 kg man that jumps out of a plane feet first? The man can be thought of as a rectangular box with dimensions 20 cm * 40 cm * 1.8 m

I tried equation v terminal = sq rt (4mg/p* area). P=1.22
I used . 72 as Area. That's wrong. Help please!

I calculated eq using .72 but that is wrong. Help!

 

[ehild]

What area should be used in the equation for terminal velocity?

ehild

 

[sona1177]

See my book says to use the cross sectional area. The answer is supposed to be 170 m/s but I am very frustrated because I can't see how they got that. His cross sectional area is 1.8 m * .40m =.72 but it's wrong if you use this.

 

[sona1177]

Oh i see what you are saying, since he jumps out feet first, that means the area is .20 * .40, this side meets air resistance. If you use this in the eq the value is 170 m/s and that's the answer. Is my reasoning correct?

 

[ehild]

Oh i see what you are saying, since he jumps out feet first, that means the area is .20 * .40, this side meets air resistance. If you use this in the eq the value is 170 m/s and that's the answer. Is my reasoning correct?

Yes, that is the clue, feet first! Good job!

ehild

 

[sona1177]

Thanks for all your help!