- #1

JimiJams

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## Homework Statement

A 20g ball of clay is shot to the right at 12m/s toward a 40g ball of clay at rest. The two balls of clay collide and stick together. Call this reference frame S.

## Homework Equations

What is the velocity of a reference frame S' in which the total momentum is zero?

## The Attempt at a Solution

How I interpreted this is I calculated what velocity the 40 g ball would need to move for total momentum to equal zero. I came up with (.02kg)(12m/s)+(.04kg)(-6m/s)=0

Having found its velocity to be -6 m/s to satisfy a total momentum of zero I figured a reference frame moving 3 m/s would make the 20 g ball appear like it was traveling at 9 m/s and the 40 g ball at -9 m/s.

But this still doesn't sit right with me. I don't know why I went through the trouble of making their velocities appear equal but opposite, it seems unnecessary.

So my other though is maybe they mean the total momentum of the reference frame should be zero in which case the reference frame would simply have a velocity of 0 m/s.

Do either of these sound right? The wording of the question seems to complicate things.

Thanks in advance