Calculating Inertia Ratios of Carts on a Low-Friction Track

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Homework Help Overview

The discussion revolves around calculating the inertia ratios of two carts, A and B, involved in a collision on a low-friction track. Participants are analyzing the relationship between the masses of the carts based on their velocity changes during the collision.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are questioning the reasoning behind the initial ratio of 1/2 and discussing which cart has the larger mass based on observed changes in speed. There is an exploration of how to estimate the inertia ratios from the provided velocity curves.

Discussion Status

The discussion is ongoing, with participants expressing confusion over the correct ratio and the methodology for determining it. Some have suggested that the ratio should be close to 2/1, while others have pointed out contradictions in the reasoning presented. There is a recognition of the challenges posed by the problem statement.

Contextual Notes

Participants note that measuring individual pixels from the velocity curves may not be appropriate for this type of problem, leading to further confusion regarding the expected approach and the accuracy of their estimates.

emily081715
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Homework Statement



The vx(t) curves for two carts, A and B, that collide on a low-friction track are shown below:
Mazur1e.ch4.p10.jpg

What is the ratio of their inertias?

Homework Equations


the ratio i am looking for is mB/mA

The Attempt at a Solution


I believed that the ration was 1/2 however that is not correct and i do not see how there can be another ratio
 
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How did you get the value 1/2?
Which mass is larger?
 
mfb said:
How did you get the value 1/2?
Which mass is larger?
is the cart of mass B not larger because it had a smaller change is speed, meaning it has a larger inertia and greater mass. i got the 1/2 ratio because the mass of cart A is double the mass of cart B
 
emily081715 said:
is the cart of mass B not larger because it had a smaller change is speed, meaning it has a larger inertia and greater mass.
Correct, cart B has a larger mass.
emily081715 said:
because the mass of cart A is double the mass of cart B
This is in contradiction to what you said immediately before that.
 
I meant cart B is double the mass of cart A. But the ratio isn't 2/1
 
emily081715 said:
But the ratio isn't 2/1
Why not?
You can try to estimate the changes a bit better from the diagram, that will give a value very close to 2/1, but usually you are not supposed to measure individual pixels on problems like this.
 
mfb said:
Why not?
You can try to estimate the changes a bit better from the diagram, that will give a value very close to 2/1, but usually you are not supposed to measure individual pixels on problems like this.
i already tried the ratio and it was wrong which is why I'm confused for the question
 
emily081715 said:
i already tried the ratio and it was wrong which is why I'm confused for the question
turns out the answer was 2.1
 
Okay, bad problem statement. Giving something that is so close to 2 and then expecting students to count pixels is a very bad style.
 

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