Considerations for the FBDs of a parachutist traveling at terminal velocity

In summary, the force from the parachutist consists of their weight and the weight of their gear, and at terminal velocity, the sum of all forces is zero. The force from the parachutist on the parachute is the total tension in the ropes that tether them together. The equation for the third law is ##P=N##.
  • #1
greg_rack
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Homework Statement
I'll attach the statement below since it consists of a free-body diagram
Relevant Equations
##F=ma##
##W=mg##
Schermata 2020-10-21 alle 22.01.04.png
There are a few things I'm not getting about this exercise and related diagram:
-what does "force from parachutist" consists of?
-if the terminal velocity is reached, then ##a=0## which means ##F_{tot}=0##, so shouldn't simply the sum of all forces pointing upwards be equal to the sum of all pointing downwards?
 
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  • #2
greg_rack said:
Homework Statement:: I'll attach the statement below since it consists of a free-body diagram
Relevant Equations:: ##F=ma##
##W=mg##

View attachment 271329
There are a few things I'm not getting about this exercise and related diagram:
-what does "force from parachutist" consists of?
-if the terminal velocity is reached, then ##a=0## which means ##F_{tot}=0##, so shouldn't simply the sum of all forces pointing upwards be equal to the sum of all pointing downwards?
The force from parachutist is just their weight and the weight of all of their gear.

And you are correct, at terminal velocity, there is no acceleration of the parachutist and parachute -- they both fall at the constant terminal velocity. So the sum of all forces is zero in that state.
 
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  • #3
berkeman said:
The force from parachutist is just their weight and the weight of all of their gear.
No, it is the force the parachutist and clothing etc. exerts on the parachute.
greg_rack said:
shouldn't simply the sum of all forces pointing upwards be equal to the sum of all pointing downwards?
Yes... are you saying that, according to the exercise, it is not?
But what are you selecting as the answer to the question?
 
  • #4
greg_rack said:
-what does "force from parachutist" consists of?
Call it the total tension in the ropes that tether the parachutist to the parachute. Note that the upper part of the ropes is in the FBD of the parachute and the lower part of the ropes is in the FBD of the parachutist. Does that help?
 
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  • #5
kuruman said:
Does that help?
That definitely helped, now I’m understanding the situation much better!
But, shouldn’t either ##P=N## and ##M+R=L+Q##?
 
  • #6
greg_rack said:
That definitely helped, now I’m understanding the situation much better!
But, shouldn’t either ##P=N## and ##M+R=L+Q##?
##M+R=L+Q## is " more "second law than third law too me, even if it is true, the question want 3rd Law's implications
 
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  • #7
LCSphysicist said:
##M+R=L+Q## is " more "second law than third law too me, even if it is true, the question want 3rd Law's implications
God, I’ve totally missed it... what a fool!
I was thinking in terms of the second law :)
Well, the equation is ##P=N## then, right?
 
  • #8
greg_rack said:
God, I’ve totally missed it... what a fool!
I was thinking in terms of the second law :)
Well, the equation is ##P=N## then, right?
Yes.
 
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FAQ: Considerations for the FBDs of a parachutist traveling at terminal velocity

What is terminal velocity and how does it affect a parachutist?

Terminal velocity is the maximum speed that an object can reach when falling through a fluid, such as air. For a parachutist, this means that they will eventually reach a constant speed where the air resistance equals the force of gravity pulling them down. This is important to consider when designing a parachute system, as it determines the amount of drag and impact force that the parachutist will experience.

How does the weight of the parachutist affect their terminal velocity?

The weight of the parachutist will affect their terminal velocity as it determines the force of gravity acting on them. The heavier the parachutist, the faster they will fall and reach their terminal velocity. This is why it is important for parachutists to have a proper weight-to-surface area ratio to ensure a safe descent.

What role does air density play in the FBDs of a parachutist at terminal velocity?

Air density is a major factor in determining the FBDs (forces acting on an object) of a parachutist at terminal velocity. Higher air density means more air resistance, which will slow down the parachutist's descent and decrease their terminal velocity. This is why parachutists often jump at higher altitudes where the air is less dense, allowing them to reach higher speeds.

How does the shape of the parachute affect the FBDs of a parachutist at terminal velocity?

The shape of the parachute is crucial in determining the FBDs of a parachutist at terminal velocity. A larger surface area will create more air resistance, slowing down the descent and decreasing the impact force on the parachutist. The shape and design of the parachute also play a role in controlling the descent and ensuring a safe landing.

What other factors should be considered for the FBDs of a parachutist at terminal velocity?

Other important factors to consider for the FBDs of a parachutist at terminal velocity include the altitude and wind conditions, as these can affect the air density and wind resistance. The materials and construction of the parachute also play a role in its performance and the forces acting on the parachutist. Proper training and technique of the parachutist are also crucial for a safe and successful descent at terminal velocity.

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