# Relating Kinetic Energies and Masses of Two Objects

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## Homework Statement

Two objects of inertias m1 and m2 start from rest and then interact with each other (assume neither is interacting with any other object).
What is the ratio of their kinetic energies at any instant?

## Homework Equations

$\frac{K_{1}}{K_{2}} = ?$
The first part of the equation asked me to relate velocities to masses and I got a correct answer of

$\frac{v_{2x}}{v_{1x}} = -\frac{m_{1}}{m_{2}}$

## The Attempt at a Solution

I know that Kinetic Energy is half of the mass times the square of the velocity, and that's where my attempt falls apart, because I have to express the answer in terms of m1 and m2, but they're already in KE so I don't understand how that works out. My answer I got was

$\frac{K_{1}}{K_{2}} = \frac{m_{2}}{m_{1}}$

Without the negative cause it is the square of the velocity and that will eliminate any negatives. Please help.

nasu
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It's not okay though :( apparently I am not correct

The answer you have obtained is correct .

nasu
Gold Member
It's not okay though :( apparently I am not correct
How do you know this? What do you think is the correct answer?

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How do you know this? What do you think is the correct answer?
It's part of a homework assignment and when I put in an answer it spits out a correct or incorrect judgement. I put in my answer and it's incorrect. The professor said things like this would happen though, and when they did to come to him because we're using a new system and there are mistakes in it that he's found. I hope that is the case because I tried every combination of subscript and now they most I can get on the question is 50% for a correct answer regardless of the amount of tries.