# Ratios of inertia

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1. Sep 25, 2016

### emily081715

1. The problem statement, all variables and given/known data

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

What is the ratio of their inertias?
2. Relevant equations
the ratio i am looking for is mB/mA

3. 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

2. Sep 26, 2016

### Staff: Mentor

How did you get the value 1/2?
Which mass is larger?

3. Sep 26, 2016

### emily081715

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

4. Sep 26, 2016

### Staff: Mentor

Correct, cart B has a larger mass.
This is in contradiction to what you said immediately before that.

5. Sep 26, 2016

### emily081715

I meant cart B is double the mass of cart A. But the ratio isn't 2/1

6. Sep 26, 2016

### Staff: Mentor

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.

7. Sep 26, 2016

### emily081715

i already tried the ratio and it was wrong which is why i'm confused for the question

8. Sep 26, 2016

### emily081715

turns out the answer was 2.1

9. Sep 26, 2016

### Staff: Mentor

Okay, bad problem statement. Giving something that is so close to 2 and then expecting students to count pixels is a very bad style.