Free falling ball with and without air resistance

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Homework Help Overview

The problem involves a 2 kg ball in free fall, with an initial downward velocity of 12 m/s. The objective is to find the difference in displacement after 1 second, comparing scenarios with and without air resistance, while incorporating a "k factor" related to air resistance.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the need to define the "k factor" for air resistance, noting that it is not standard terminology. There are questions regarding the appropriateness of the units for k and how they relate to the modeling of air resistance.

Discussion Status

There is ongoing exploration of the definitions and implications of the "k factor." Participants are questioning the units and their relevance to the problem, indicating a lack of clarity that needs to be addressed before proceeding further.

Contextual Notes

Participants highlight that the units for the k factor are unusual and suggest that air resistance is typically modeled differently, indicating potential misunderstandings or miscommunications regarding the problem setup.

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Homework Statement


A 2 kg ball (k factor of 0.02 m-1) is in free fall. The initial downward velocity of the ball is 12 m/s. Find the difference in displacement after 1s both with and without air resistance.

Homework Equations


vf = vi + at
y = yi + 1/2(vi+vf)t
y - yi = vit + (1/2)At2 - (1/3)Bt3
F = ma

The Attempt at a Solution


I have determined the displacement of the ball without air resistance to be -16.9m by first finding the final velocity after 1s:
vf = vi + at
= -12 + (-9.8)(1s)
= -21.8m/s

And then the final displacement:
y - yi = vit + (1/2)At2 - (1/3)Bt3
= 1/2(-12-21.8)(1s)
= -16.9m

However, I am unable to figure out how to find the displacement of the ball with air resistance present and how to incorporate the k factor. So far, I have determined:
F = (2kg)(-9.8)
= -19.6N

Not sure where to go from here :(
 
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They need to define the "k factor" for the air resistance. That is not standard terminology, and it needs to be defined in order to proceed.
 
Charles Link said:
They need to define the "k factor" for the air resistance. That is not standard terminology, and it needs to be defined in order to proceed.
It also looks a little suspicious that the units for k are given as ##[m^{-1}]##, since generally air resistance is modeled as being proportional to either ##v## or the square of ##v##.
 
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gneill said:
It also looks a little suspicious that the units for k are given as ##[m^{-1}]##, since generally air resistance is modeled as being proportional to either ##v## or the square of ##v##.
If we take the units on trust, for factor × something = force the something has to have units of energy. KE maybe? Weird.
 
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