# Elastic Collision Questions: Greatest KE & Unequal Mass

• strag
In summary: I'll have to think about that.In summary, the conversation discusses two scenarios involving collisions and the transfer of kinetic energy. In the first scenario, two objects collide in an elastic collision and the question is when the greatest KE is transferred. In the second scenario, two objects with unequal mass are at rest and have equal forces acting on them for equal amounts of time. The question is what the object with greater mass will experience when these forces are removed. The conversation also discusses the role of mass and velocity in determining the amount and percentage of KE transferred.
strag

## Homework Statement

A. Two objects collide in elastic collision (one is at rest). When is the greatest KE transferred?

B. Two objects w/unequal mass are at rest (frictionless surface) and have equal forces acting on them for equal amts of time. When these forces are remove, what will the object with greater mass experience?

## The Attempt at a Solution

A. Since masses are conserved, wouldn't the only variable change is the velocity? So shouldn't it be where the moving object is traveling very fast, or does this question involve mass?

B. I used equation F=p/t. If the forces are equal and so is time, wouldn't the momentum be the same for both? Considering the surface is frictionless.

strag said:
A. Since masses are conserved, wouldn't the only variable change is the velocity? So shouldn't it be where the moving object is traveling very fast, or does this question involve mass?
I'd say that the question involves mass.

B. I used equation F=p/t. If the forces are equal and so is time, wouldn't the momentum be the same for both? Considering the surface is frictionless.
Yes, the momentum is the same. So what can you say about the object with greater mass?

Doc Al said:
I'd say that the question involves mass.Yes, the momentum is the same. So what can you say about the object with greater mass?

For the first one though, since ke=1/2 m v^2, shouldn't the velocity have the greatest effect on KE since it's a squared variable?And p=mv...so larger mass should have a smaller velocity.

strag said:
For the first one though, since ke=1/2 m v^2, shouldn't the velocity have the greatest effect on KE since it's a squared variable?
The question is vaguely worded. What I think they are looking for is under what conditions (consider the relative masses of the objects) will the greatest percentage of KE be transferred. That has a clearcut answer.

And p=mv...so larger mass should have a smaller velocity.
That's what I would say.

Doc Al said:
The question is vaguely worded. What I think they are looking for is under what conditions (consider the relative masses of the objects) will the greatest percentage of KE be transferred. That has a clearcut answer.

That's what I would say.

Sorry I'll try to reword it.

Two objects (A and B) have the same momentum. A has more kintetic energy than B if

1. it is heavier than B.
2. it has a higher speed than B.

My reasoning is that it would be #2 b/c of the squared factor I mentioned. Having a larger mass would mean a smaller speed for A and if u have a smaller speed it would be squared, resulting in a smaller KE than if u would be increasing the speed.

strag said:
Sorry I'll try to reword it.
I didn't mean that your question (in your last post) was vaguely worded, but that the question in the problem statement for A was.

What I gave is my guess as to what they are looking for.

One more question if you don't mind helping!

A object (A) has an elastic collision with another object (B) initially at rest. Greatest KE is transferred if:

A is traveling really fast.

A weighs a lot more than B.

Isn't the same thing...just look at the KE=1/2 m v^2? Having a faster velocity (squared value) is better than mass.

I don't think that's what they are looking for. I suspect they want the conditions under which the greatest percentage of KE transferred, not the greatest amount. The velocity doesn't matter.

Doc Al said:
I don't think that's what they are looking for. I suspect they want the conditions under which the greatest percentage of KE transferred, not the greatest amount. The velocity doesn't matter.

I'm having difficulty understanding why velocity wouldn't matter. And yes you're right about the fraction/percentage.

## 1. What is an elastic collision?

An elastic collision is a type of collision where both kinetic energy and momentum are conserved. This means that no energy is lost during the collision and the total momentum of the system remains the same before and after the collision.

## 2. What is the equation for calculating kinetic energy in an elastic collision?

The equation for calculating kinetic energy in an elastic collision is KE = (1/2)mv^2, where m is the mass of the object and v is its velocity.

## 3. How do you determine the greatest kinetic energy in an elastic collision?

The greatest kinetic energy in an elastic collision is determined by finding the object with the highest mass and velocity. This object will have the most kinetic energy.

## 4. Can kinetic energy be transferred between objects in an elastic collision?

No, kinetic energy cannot be transferred between objects in an elastic collision. It remains constant and is only redistributed between the objects involved.

## 5. How does the mass of the objects affect the kinetic energy in an elastic collision?

The mass of the objects directly affects the kinetic energy in an elastic collision. The object with the higher mass will have a greater kinetic energy compared to the object with a lower mass, even if they have the same velocity.

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