Seemingly simple mechanics questions

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Homework Help Overview

The problem involves a box with weight mg and a string exerting a tension t, where the tension is less than the weight. The original poster seeks to understand the conditions under which the box can rise with a decreasing speed and fall with an increasing speed, as described in the problem statement.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to analyze the situation by considering the implications of negative acceleration and the relationship between tension and weight. Some participants question the assumptions about the initial state of the system, suggesting that the box may not have been at rest initially.

Discussion Status

The discussion is ongoing, with participants exploring various scenarios that could lead to the described behaviors of the box. There is a recognition of the ambiguity in the problem statement, and some guidance is being offered regarding the initial conditions that could affect the box's motion.

Contextual Notes

Participants note the constraint that the tension t is less than the weight mg, which influences the dynamics of the system being discussed.

werproc
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1. Homework Statement
The problem basically states that there is a box with weight mg and a string that is less of magnitude with tension t as shown in this picture: https://gyazo.com/efeb48469cfb44399bea6c2dcc9e87c7
The question is what are two possibilities for this situation and the answers are : rising with a decreasing speed and falling with an increasing speed. I do not understand the rising with a decreasing speed aspect of it in conceptual and mathematical terms. How does this happen (in what scenario for example)?

Homework Equations

:
F=ma, mg etc.[/B]

The Attempt at a Solution


It's obvious that acceleration is negative from the start as mg has the greater magnitude (T-mg/m = a)
my thought was we either have an initial tension that decreases of some sort or we have an initial velocity above 0 for the box and it decreases as time goes on
 
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werproc said:
It's obvious that acceleration is negative from the start as mg has the greater magnitude (T-mg/m = a)
my thought was we either have an initial tension that decreases of some sort or we have an initial velocity above 0 for the box and it decreases as time goes on
Do not assume the system was previously at rest, with only mg and T<mg acting on it since. The object may have been given an initial speed by some some larger T, or by some other means.
 
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That problems seems somewhat unspecific

I can think of scenarios in which at least the last two answers apply and possible the first two as well

I am curious as to what the answer is and why
 
Kaura said:
That problems seems somewhat unspecific
I can think of scenarios in which at least the last two answers apply and possible the first two as well
I am curious as to what the answer is and why
Note the constraint mentioned here:
werproc said:
weight mg and a string that is less of magnitude with tension t
 

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