# Changing the inertial reference frame to follow a mass in a collision

• Backup
In summary, the question is discussing the potential downside of using an inertial reference frame in solving elastic collision problems in one dimension. The equations Vf1 and Vf2 can be simplified if a different inertial reference frame is chosen, but there may be a risk of forgetting to convert back to the initial frame of reference when computing energy.
Backup

## Homework Statement

We could change to inertial reference frame in a collision to follow a mass. But what would the down side be if we did?

## Homework Equations

Vf1=(M1-M2)/(M1+M2)*Vi1 +2M2/(M1+M2)*Vi2

Vf2=2M1/(M1+M2)*Vi1 +(M1-M2)/(M1+M2)*Vi2

## The Attempt at a Solution

This question appears too simple and my teacher doesn't want to even tell me I'm partially right. But it seems that if you followed one mass the final velocity would be higher it actually is, it is higher by the speed of the object that we follow. If you play around with the equation you see that this is true... i think.
So am I right or wrong. And, if I'm right, what am I missing?

Are you really changing the inertial frame of reference? For instance, my measurement of both velocities could be off if I were in motion. Say one of the masses and I were moving at the same rate, it would appear motionless just as cars do when traveling at the same speed. So what you consider an absolute velocity doesn't really matter, so long as all are in the same inertial frame of reference and the relative velocities are accurate.

In fact all objects could be subject to uniform acceleration--say in free fall and momenta would be still conserved.

This is the actual question
"Discuss how the two equations might be simplified if we choose a different inertial reference frame for some problem under consideration. Explain the potential downside in taking this approach in solving elastic collision problems in one dimension."

Ok I think see what he wants: did you derive the above equations yourself or look them up.

You might try deriving those in 2 different cases: when both masses have non-zero velocities and then again when one mass has an initial velocity of zero. The latter is not too bad, the former derivation is fairly ugly. The drawback may be in forgetting to convert back to the initial frame of reference when computing energy.

## 1. What is an inertial reference frame?

An inertial reference frame is a coordinate system that remains at rest or moves with a constant velocity in a straight line. It is used to measure motion and describe the laws of physics.

## 2. Why is it important to change the inertial reference frame in a collision?

In a collision, the initial and final velocities of objects can change. Changing the inertial reference frame allows us to better understand and analyze the motion of objects involved in the collision, and calculate important quantities such as momentum and kinetic energy.

## 3. How is the inertial reference frame changed in a collision?

The inertial reference frame can be changed by choosing a new coordinate system that is more convenient or useful for analyzing the collision. This can involve rotating or shifting the original coordinate system to align with the motion of the objects involved in the collision.

## 4. What is the role of mass in changing the inertial reference frame in a collision?

The mass of an object determines the amount of force required to change its motion. In a collision, the mass of the objects involved influences how they interact and how the inertial reference frame should be changed to accurately describe the motion of the objects.

## 5. How does changing the inertial reference frame affect the conservation of energy and momentum in a collision?

The conservation of energy and momentum are fundamental laws of physics that hold true in all inertial reference frames. Changing the inertial reference frame in a collision does not affect these principles, as long as the new frame is properly chosen and the laws of physics are applied correctly.

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