Calculating Collision Speed: Momentum or Kinetic Energy?

AI Thread Summary
To determine the speed of a lighter object needed for both to stop after a collision, momentum conservation is the key principle, as total momentum must equal zero. Kinetic energy is not conserved in this scenario because the collision is inelastic. While both momentum and energy conservation can be used theoretically, momentum simplifies calculations in many cases. It is important to consider that total energy encompasses various forms, including heat and potential energy. Therefore, using conservation of momentum is generally the most effective approach for this problem.
2sin54
Messages
109
Reaction score
1
Hi. Sorry if this looks too beginner-ish question.

Lets say we have two objects moving towards each other. One is heavier than another and we know it's speed. We want to find out how fast should lighter object move so that after the collision both objects would stop.

Question is, what should we use to calculate the speed of the lighter body, kinetic energy's equation or momentum's? Those two give slightly different answers.

Thank you.
 
Physics news on Phys.org
If you want the objects to stop after they collide, the total momentum must be zero. Kinetic energy will not be conserved, since the collision must be inelastic. (Momentum is always conserved.)
 
Momentum is always conserved and total energy is always conserved, so you can use either one in principle. But total energy includes kinetic energy, heat energy lost due to friction, potential energy, etc. so it is easier in many problems to use conservation of momentum. Note that if there are enough unknowns, you may need to use both conservation of energy and momentum.
 
  • Like
Likes Eddie Sines

Thread 'Is calling fictitious forces "not real" just about terminology?'

Hi there, im studying nanoscience at the university in Basel. Today I looked at the topic of intertial and non-inertial reference frames and the existence of fictitious forces. I understand that you call forces real in physics if they appear in interplay. Meaning that a force is real when there is the "actio" partner to the "reactio" partner. If this condition is not satisfied the force is not real. I also understand that if you specifically look at non-inertial reference frames you can...
View full post »

Thread 'Derivation of Hamilton's Principle: Questions'

I have recently been really interested in the derivation of Hamiltons Principle. On my research I found that with the term ##m \cdot \frac{d}{dt} (\frac{dr}{dt} \cdot \delta r) = 0## (1) one may derivate ##\delta \int (T - V) dt = 0## (2). The derivation itself I understood quiet good, but what I don't understand is where the equation (1) came from, because in my research it was just given and not derived from anywhere. Does anybody know where (1) comes from or why from it the...
View full post »

Similar threads

I Question about Momentum vs. Kinetic Energy vs. Deforming In Collisions
Replies
2
Views
2K
B Colliding balls: Conservation of momentum and changes in kinetic energy?
Replies
2
Views
2K
I Torque and Rotational Kinetic Energy Relationship
Replies
4
Views
2K
I Work Done/Energy Transferred in One Dimensional Collision
Replies
5
Views
2K
How Do Momentum and Kinetic Energy Influence Collision Outcomes?
Replies
12
Views
2K
B About verification on Kinetic energy and work
Replies
16
Views
2K
I Why is momentum considered a vector and kinetic energy a scalar?
Replies
15
Views
3K
Energy transformed in a collision
Replies
5
Views
2K
Why do heavier projectiles tend to have higher momentum?
Replies
29
Views
6K
I Question about transfer of Energy and Momentum in Ballistics
Replies
34
Views
4K

Hot Threads

Recent Insights

Back
Top