- #1
angryzeena
- 8
- 0
Homework Statement
Homework Equations
Fn - T = ma
The Attempt at a Solution
Fn-T=ma
810kg x 2.5m/s2 - T = 810 kg x -2.5m/s2
T=0
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SUMMARY
The discussion focuses on calculating the tension in a parachute cord attached to a dragster, using the equation Fn - T = ma. Participants clarify that the net force acting on the dragster is not zero, as the parachute exerts a force of -2025 N, which is essential for deceleration. The confusion arises from misinterpreting the role of tension and net force, ultimately concluding that the tension cannot be zero if the parachute is functioning correctly. The correct interpretation of the forces leads to the realization that the tension is indeed 2025 N, which aligns with the expected answer when rounded to two significant digits.
PREREQUISITES- Understanding of Newton's Second Law (F = ma)
- Familiarity with forces acting on objects (gravity, normal force, tension)
- Basic knowledge of significant figures in physics
- Experience with free-body diagrams and net force calculations
- Study the concept of net force and its calculation in various scenarios
- Learn about free-body diagrams and their application in physics problems
- Explore the role of tension in different systems, such as pulleys and cables
- Review significant figures and rounding rules in scientific calculations
Students studying physics, educators teaching mechanics, and anyone interested in understanding forces and motion in practical applications like drag racing.
Fn - T = ma
Fn-T=ma
810kg x 2.5m/s2 - T = 810 kg x -2.5m/s2
T=0
- #2
- 42,799
- 10,495
What is this force "Fn"?
- #3
angryzeena
- 8
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sorry couldn't type subscript. It is the net force.
- #4
- 42,799
- 10,495
The net force is the sum of all the applied forces. What are the applied forces?angryzeena said:
The acceleration is what results from the net force: ##F_{net}=\Sigma F = ma##.
- #5
angryzeena
- 8
- 0
applied forces are:
-2025 kgm/s2 from the parachute
I have a feeling we are missing other applied forces.
-2025 kgm/s2 from the parachute
I have a feeling we are missing other applied forces.
- #6
- 42,799
- 10,495
No, that is the only force of interest. (There is gravity and the normal force from the ground, but they cancel out.)angryzeena said:
So what is the net force? What equation does that give you?
- #7
angryzeena
- 8
- 0
ok so - tension is the force transmitted through the cord on the object. Force of gravity and normal upward force are equal so cancel out but we are trying figure out horizontal force not vertical force anyways.
We are lost...
We are lost...
- #8
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
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You should ask yourself, if the tension in the parachute line is truly equal to zero, then why have the parachute attached to the dragster at all? What is the parachute doing?angryzeena said:
angryzeena said:
Isn't the correct form of this equation Fnet = ma ?
By putting the deceleration force on both sides of the equation, how else can T be anything but zero?
- #9
angryzeena
- 8
- 0
exactly what we thought - T cannot be zero as it wouldn't be doing any work.
So then we thought T = net force on the object = ma = 810 kg x 2.5 m/s2 but that seems to be incorrect? Why?
So then we thought T = net force on the object = ma = 810 kg x 2.5 m/s2 but that seems to be incorrect? Why?
- #10
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
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How do you know it's incorrect?angryzeena said:
- #11
angryzeena
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haruspex said that was only the force of interest not the net force. Also 2025 N is not one of the options for an answer.
- #12
- 42,799
- 10,495
Does it not match any of the offered answers? The choices are only specified to two significant digits, so round your answer accordingly and then compare. What do you get?angryzeena said:
- #13
- 42,799
- 10,495
I didn't say it was not the net force. If it's the only force of interest then it is the net force.angryzeena said:
And 2025 N is one of the answers (see my preceding post).
- #14
angryzeena
- 8
- 0
ah ha it is becoming clearer. I appreciate you making me think.
- #15
angryzeena
- 8
- 0
It has been many years since physics 12 - I am helping my daughter. She and I will laugh in the morning over thinking that 2025 N does not equal 2.0x10 to the third when rounded. Many thanks...
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