Solving 2 Mass System w/o Diagram: Find Acceleration, Force & Time

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Homework Help Overview

The problem involves two masses, 0.5 kg and 0.8 kg, connected by a string over a frictionless pulley. Participants are tasked with finding the acceleration of the 0.5 kg mass, the net force on the 0.8 kg mass, and the time to reach a specific velocity, all without a diagram.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Some participants question whether the problem can be solved without a diagram, suggesting that a free body diagram would clarify the forces involved.
  • Others discuss the assumptions regarding the setup, including the direction of movement for each mass and the nature of the pulley system.
  • There are mentions of using Newton's laws and energy equations to approach the problem, but the lack of a visual aid is noted as a potential barrier.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem setup and the implications of their assumptions. Some guidance has been offered regarding the use of free body diagrams and the application of Newton's laws, but no consensus has been reached on a definitive approach.

Contextual Notes

Participants note the absence of a diagram as a significant constraint, which may affect their ability to visualize the forces at play. There are also discussions about the assumptions related to the pulley and the string's properties.

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Homework Statement


Two objects of mass 0.5kg and 0.8kg respectively are connected by a light string that passes over a frictionless pulley. Find:
a) the acceleration of the 0.5kg mass
b) the net force acting on the 0.8kg mass
c) the time taken for the masses to reach a velocity of 2.8m/s


Homework Equations


Newton's laws


The Attempt at a Solution


The question was given without a diagram. Is it possible to do this problem just from the data above without a diagram?
 
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pivoxa15 said:

Homework Statement


Two objects of mass 0.5kg and 0.8kg respectively are connected by a light string that passes over a frictionless pulley. Find:
a) the acceleration of the 0.5kg mass
b) the net force acting on the 0.8kg mass
c) the time taken for the masses to reach a velocity of 2.8m/s


Homework Equations


Newton's laws


The Attempt at a Solution


The question was given without a diagram. Is it possible to do this problem just from the data above without a diagram?
A diagram would be helpful. I believe the problem assumes a pulley attached to a ceiling, with the masses hanging down from either side. The 0.8 kg mass will move downward, and the 0.5 kg mass moves up. Draw free body diagrams of each mass and identify the forces acting on each, then apply Newton 2 to determine the acceleration of each from the net force acting on each.
 
Object 1: 0.5 kg
Object 2: 0.8 kg

Tension relates the two objects =).

There needs to be a force body diagram to get an idea of how the forces are working. But, without it you can get a basic idea of how it looks in your head and be able to solve it.

Acceleration of the system = [ (object 1 - object 2) / (object 1 + object 2) ] * gravity

1/2mv^2 and mgh are your tools when dealing with energy =). They can also be tied with vectors.

Using the equations: x = xo + volt + 1/2at^2, v2^2 = v2o^2 + 2a(x2 - x1) and v = vo + at.

It is possible.
 
PhanthomJay said:
A diagram would be helpful. I believe the problem assumes a pulley attached to a ceiling, with the masses hanging down from either side. The 0.8 kg mass will move downward, and the 0.5 kg mass moves up. Draw free body diagrams of each mass and identify the forces acting on each, then apply Newton 2 to determine the acceleration of each from the net force acting on each.

The answers did assume that the weights were spread from both sides downwards. Each mass has the same acceleration and tension because they are connected by strings so are considered linked. We assume the string cannot be stretched nor dangled do we?
 
pivoxa15 said:
The answers did assume that the weights were spread from both sides downwards. Each mass has the same acceleration and tension because they are connected by strings so are considered linked. We assume the string cannot be stretched nor dangled do we?
Right, and we assume the pulley does not actually spin. When the pulley rotates, you have to factor in friction and moment of inertia of the wheel
 

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