Solving a Homework Problem with Mass, String, and Friction

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Homework Help Overview

The problem involves two blocks of mass m_{A} and m_{B} connected by an ideal string, with block A descending at a constant speed and no friction present. The context suggests a focus on the forces acting on the blocks and the implications of constant speed in relation to Newton's laws and trigonometry.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to analyze the forces acting on the blocks, questioning the correctness of the marked answer based on their reasoning about constant speed and force balance. Some participants provide quick confirmations of the original poster's conclusions, while others suggest a method involving the sine components of gravitational forces.

Discussion Status

The discussion appears to be progressing with participants affirming the original poster's reasoning and providing brief confirmations of correctness. There is an exploration of different interpretations of the problem, but no explicit consensus has been reached.

Contextual Notes

Participants note the potential for errors due to quick calculations and the original poster's mention of typing difficulties, which may affect clarity in communication.

SqueeSpleen
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Homework Statement


There's two blocks of mass m_{A} and m_{B} which are linked by an ideal string. The block of mass A descends at constant speed. There's no friction. If the pulley is ideal, which one of the following is true[/B]
upload_2017-5-19_0-33-15.png

Homework Equations


Newton laws and trigonometry I think.[/B]

The Attempt at a Solution


I think that the correct answer is the second one, but the first one is marked as correct so I wanted a second opinion.
My reasoning is the following: If the speed is constant it means there is no acceleration, so the sum of the forces is 0. Then I decomposed gravity in the component that's compensated by the normal force done by the triangle and it's perpendicular component. So I arrived to
m_{A} (1/2) = m_{B} sqrt(3)/2
Now that I check, it isn't item 2. it would fall in item 1 as 1/sqrt(3) is between 0.25 and 0.6
Right?

sorry for the typos, I broke my keyboard yesterday (I won't drink coffee while on computer again) and I'm with a rubber one until a new one arrives, at least it's better thanthe one that windows have to use with the mouse.

[/B]
 

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Working it out very quickly, and thus prone to error, I think the first answer is correct.
 
SqueeSpleen said:
it would fall in item 1 as 1/sqrt(3) is between 0.25 and 0.6
Right?
Yes.
 
Absolutely correct! Way of solving by simply taking their Sine components of 'g' and solve it.
 

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