Terminal velocity in a viscous medium

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Homework Help Overview

The discussion revolves around a physics problem involving terminal velocity in a viscous medium. The original poster presents a scenario where an object falls through a medium, experiencing a resistive force dependent on its velocity. The problem includes determining terminal speed, time to reach a specific fraction of that speed, and distance traveled in a given time frame.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants explore equations of motion relevant to the problem, questioning the applicability of constant acceleration equations. There is also an attempt to derive the distance traveled using a specific formula, leading to confusion about its correctness.

Discussion Status

The discussion is active, with participants questioning the validity of certain equations and interpretations of motion under the influence of a resistive force. Some guidance is offered regarding the nature of acceleration in this context, but no consensus has been reached on the correct approach or solution.

Contextual Notes

Participants are navigating the complexities of motion in a viscous medium, with specific attention to the effects of resistive forces and the implications for acceleration. There is a noted lack of clarity regarding the initial conditions and the assumptions made in the problem setup.

shiri
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A 11.00 kg object starting from rest falls through a viscous medium and experiences a resistive force R = -bv, where v is the velocity of the object. The object reaches one half its terminal speed in 5.84 s.

(a) Determine the terminal speed.
82.7 m/s

(b) At what time is the speed of the object three-fourths the terminal speed?
11.7 s

I couldn't figure out on this question. can someone help me out, i'll be appreciated
(c) How far has the object traveled in the first 5.84 s of motion?
 
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Can you write an equation of motion for the object?
 
Hootenanny said:
Can you write an equation of motion for the object?

was it v = [Initial velocity] + [(1/2)at^2]?
 
shiri said:
was it v = [Initial velocity] + [(1/2)at^2]?
That equation is only valid for constant acceleration, but is the acceleration constant in this case?
 
well what i got for this question is x=d=mgt/b + m^2g/b^2 * (exp(-bt/m) - 1)=483m
but I don't understand why this is a wrong answer so can you tell me why?
 

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