How Much Weight Can a 20.0 m³ Meteorological Balloon Lift?

[chawki]

Yes. That is the equation that describes the situation put forth in the problem statement. So you should be able to solve for the weight of the cargo, right?

i found that by applying second law of Newton at a statioanary state...
but you didn't answer what i asked in post#43

 

[gneill]

i found that by applying second law of Newton at a statioanary state...
but you didn't answer what i asked in post#43

What did you ask? You said:

"in post#23 you said the buoyant force is 231.51 N
isn't 128.505 N ?"

That question is answered! The buoyant force is 231.51 N, the weight of the displaced air.
It is not 128.505 N, the weight of the displaced air minus the weight of the balloon; that is the lift.

I cannot see how to make it any clearer. The only forces of interest are the buoyant force, the weight of the balloon, the lift (buoyancy - weight of balloon), and the weight of the cargo (which is set equal in magnitude to the lift for this problem).

 

[chawki]

What did you ask? You said:

"in post#23 you said the buoyant force is 231.51 N
isn't 128.505 N ?"

That question is answered! The buoyant force is 231.51 N, the weight of the displaced air.
It is not 128.505 N, the weight of the displaced air minus the weight of the balloon; that is the lift.

I cannot see how to make it any clearer. The only forces of interest are the buoyant force, the weight of the balloon, the lift (buoyancy - weight of balloon), and the weight of the cargo (which is set equal in magnitude to the lift for this problem).

NOW IT'S CLEAR...because i have been working with the idea of:
buoyancy force=weight of displaced air - weight of ballon
which is WRONG