How Does Air Speed Affect Aircraft Weight?

[Mowgli]

Homework Statement

Air (density= 1.29 kg/m^3) passes over the top surface of an aircraft whoe effective wing surface area is 75.5 m^2 at a speed of 255 m/s. If the air speed beneath the wings is 135 /s, what is the weight of the plane.

Homework Equations

W=mg

The Attempt at a Solution

I know how to find the "lift" in Newtons due to Bernoulli's effect- but I am thrown off by this question. What is the weight? Please help!

 

[phyzguy]

If you know how to find the lift in Newtons pushing upward on the plane, then ask what is the force of gravity in Newtons pulling the plane downwards? In stable flight these two are equal.

 

[Mowgli]

I'm sorry- I am not good at this. Are you saying the lift is the same as the weight?

 

[phyzguy]

Yes. Assuming that the airplane is in level flight and neither ascending nor descending, then the lift equals the weight. Just like when you are standing on the floor - the floor is pushing up on you with a force which exactly balances your weight. Otherwise you would be falling, since F=ma.

 

[Mowgli]

Right, that makes sense- thank you so much!