Law of conservation of kinetic energy?

Click For Summary

Homework Help Overview

The discussion revolves around the concepts of conservation of energy and kinetic energy, with participants exploring the differences between these laws and their implications in various scenarios, particularly in collisions and elastic potential energy contexts.

Discussion Character

  • Conceptual clarification, Assumption checking, Exploratory

Approaches and Questions Raised

  • Participants question the existence of a specific "law of conservation of kinetic energy" and discuss the implications of kinetic energy not being conserved in inelastic collisions.
  • There are attempts to relate the conservation of energy to practical examples, such as explosions and collisions, while also exploring the relationship between elastic potential energy and kinetic energy.
  • Some participants express confusion regarding the spring constant and its role in energy conservation calculations, prompting further inquiries about the relationship between force, displacement, and the spring constant.

Discussion Status

The conversation is ongoing, with participants sharing insights and clarifications about energy conservation principles. Some guidance has been offered regarding the spring constant and its significance in energy calculations, but multiple interpretations and uncertainties remain regarding the application of these concepts.

Contextual Notes

Participants are navigating through various assumptions about energy conservation in different types of collisions and the definitions of key terms, such as the spring constant, which may not be fully understood or available to all. There is also a mention of needing specific values for calculations, which may not be provided in the context of their homework.

Dynamite
Messages
27
Reaction score
0
Is there a difference between the "law of conservation of energy" and "law of conservation of kinetic energy?" If so what is it?

and what IS the law of conservation of kinetic energy? It doesn't seem to be in my textbook or on the net..
 
Physics news on Phys.org
That's because it doesn't exist. Kinetic energy is not conserved. Two blobs of equal mass hit at equal velocity and stick together. The resulting blob has no kinetic energy. Poof. Kinetic energy all gone.
 
o dear. sigh. I have a lot more to worry about now
thanks
 
Here is an example of the conservation of energy.

Say a bomb explodes. Initially, the bomb has chemical energy. When it explodes, the types of energy present are heat,light and sound. But energy neither made or destroyed, so it had to come from the chemical energy.
So applying the law of conservation of energy, you'd say that
Chemical energy -> heat+light+sound

For kinetic energy. If two bodies collide and kinetic energy is conserved, then the kinetic energy before impact =kinetic energy after impact. Kinetic energy is conserved in elastic collisions.
 
ok ok hold on, my question here is though
I have 2 carts with springs at the back of them and I've pushed them together and realeased
Then in order to prove that energy has been conserved, I'd need to calculate the elastic potential energy right..?
 
Yes. Total energy is conserved. The initial elastic potential energy must equal the final kinetic energy.
 
o goodness. Yes I DO have a lot more to worry about.
Which means I need to find the spring constant.
What does the K mean? in F=k delta x ? Is there a way I can find x with info only about force? I'm not sure I even have k...
 
Dynamite said:
o goodness. Yes I DO have a lot more to worry about.
Which means I need to find the spring constant.
What does the K mean? in F=k delta x ? Is there a way I can find x with info only about force? I'm not sure I even have k...


The K is the spring constant. In F=kx, F= force, x=displacement, and k=the spring constant
 
Dynamite said:
o goodness. Yes I DO have a lot more to worry about.
Which means I need to find the spring constant.
What does the K mean? in F=k delta x ? Is there a way I can find x with info only about force? I'm not sure I even have k...

I think you'd better state the full problem you are working on.
 
  • #10
Hahaha. On the Standardize test last year, they actually have that as the right answer. (because the other answers definitely didn't make sense at all). Heh.k is known as the string coefficient. It is a constant that every spring has. Think of it this way...

IF I were to pull on a slinky..it would be pretty easy to stretch it. So the k value would be small. If I were to pull a car spring (made of steel and all), I wouldn't be able to do it. So the k value would be big.

It is essentially a value that take into account how tough your spring is..and adjust the force necc to stretch it appropriately.

Spring constant are usually given. In some situations, you might set up a conservation of energy (PE --> KE or vice versa) to solve for k...then calculate x, F (which ever is not known)

In reality, you can prob look up the K value online or in some physics handbook if you are doing a lab and need that value
 

Similar threads

Conservation of Momentum Problem - Mechanical and Kinetic Energies
  • · Replies 2 ·
Replies
2
Views
1K
Test question: What is true for a mechanical impact?
  • · Replies 7 ·
Replies
7
Views
1K
Energy conservation law question with capacitor
  • · Replies 8 ·
Replies
8
Views
2K
A cylinder rotating on a plane with friction and then moving across a frictionless plane to a collision
  • · Replies 1 ·
Replies
1
Views
1K
Problem with when to use Force and Energy. What compresses spring/
  • · Replies 3 ·
Replies
3
Views
2K
A problem about the laws of conservation: Bullet colliding with a wood block
  • · Replies 28 ·
Replies
28
Views
2K
Conservation of angular momentum and rotational kinetic energy
  • · Replies 2 ·
Replies
2
Views
1K
Confused about a conservation of energy problem
  • · Replies 4 ·
Replies
4
Views
2K
Runner Impulse Question: Estimate Power of Runner Leaving Blocks
  • · Replies 14 ·
Replies
14
Views
2K
Potential Energy - 2D inelastic collision - ballistic pendulum
  • · Replies 10 ·
Replies
10
Views
3K