All Questions
33 questions
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Energy conservation and Lorentz invariants [closed]
In relativistic collision theory,How can we deduce energy is conserved by using Lorentz transformation?
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2
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834
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If two objects collide and one is initially at rest, is it possible for both to be at rest after the collision?
I know that the straight answer to my question is no. Since the initial momentum is not zero, the final momentum is not zero.
What about when object A impacts object B that is rigidly fixed to earth ...
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9
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6
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3k
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Apparent kinetic energy paradox
Imagine two cars (A and B) of mass $m$ that want to destroy themselves by colliding. They need a velocity of magnitude $2v$ with respect to each other to achieve the destruction that they want and ...
- 260
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4
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598
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Centre of mass frame
I was just looking at the equation:
$$v2-v1=-e(u2-u1).$$
This equation is to describe the collision between two masses, where $v$ is the final velocity and $u$ is the initial velocity, $e$ is the ...
- 23
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6
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2k
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If a train hits a ball at $200$mph how fast does it bounce off the train?
So I'm taking some classes on Brilliant and I'm starting with the basic stuff I already know and learned in hs/ms. We come to this question where we're dealing with switching frames of reference.
Now ...
- 41
1
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2
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Is it possible to find the final velocities of two objects in a perfectly elastic one dimensional collision where both objects have initial velocity?
I'd like to know how to generally solve for final velocity of both objects after a perfectly elastic collision. Cannot be in a lab reference frame because I'm programming it. Must be able to solve ...
- 27
2
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2
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367
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What exactly happens in a rigid body collision?
Consider a situation in which a body of mass m moving with a velocity v is collided with a similar mass, applying momentum conservation,the initial mass will come to rest and the other mass will move ...
- 538
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7
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Where does the law of conservation of momentum apply?
Take the scenario of a snowball hitting a tree and stopping. Initially, the snowball had momentum but now neither the snowball nor tree have momentum, so momentum is lost (thus the law of conservation ...
- 87
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4
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Velocities in an elastic collision
My teacher keeps saying that, in a head-on elastic collision of two bodies of equal masses, the velocities get exchanged. But consider two balls of equal mass moving with the same velocity in the ...
- 1,637
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2
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305
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Why is the loss of energy maxed in perfectly inelastic collision?
I was doing a physics problem, and it had asked me to find the maximum $K_e$ loss, but I don’t understand why the loss is maxed when the objects stick together (the collision is inelastic).
user276754
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Inelastic Collision of two balls [closed]
Is it possible that two balls of the same weight collide (in 1 dimension) and then stay at the rest?
How is such a collision called?
What are all the possible situations (velocities of 2 balls of the ...
- 255
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518
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Why doesn't the speed of objects change in the reference frame of center of mass?
We often say that before and after 1-d elastic collision, one objects velocity only changes its direction in the reference frame of their centre of mass.
I can show this algebraically, writing ...
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3
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2k
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Confusion regarding a case of head-on elastic collision of two bodies of equal mass
If two bodies collide elastically, it's common to hear that the velocities, speeds and momenta are interchanged. I thought this was obvious. But if we consider two bodies moving with equal mass and ...
- 130
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74
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ENERGY TRANSFER
Why does an electron carry half the center of mass energy after undergoing RELATIVISTIC elastic scattering at 90 degress with a proton in the center of mass frame. Is there a reference that you may ...
- 21
3
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3
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956
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Why a ball doesn't stop when it collides with a wall?
If a ball collides with a ball of same mass the first ball stops and the second ball gets the velocity of first ball.The first ball stops due to the reaction force acting on it. But when a ball ...
- 315
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1
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464
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Using zero-momentum frame to solve a 2D oblique collision
How could I solve this problem using the ZMF concept? I understand how this would be done in a 1D problem, so could I apply the same logic, finding a vector that makes momentum in each direction zero, ...
- 358
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4
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108
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Momentum is not conserved during inelastic collision?
When considering room as a system, when a ball is made to fall freely and it collides with the floor it loses speed each time it collides. The momentum hence is not conserved in this case?
Can anyone ...
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2
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5
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311
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Where is the momentum going?
When a ball of mass $m$ collides elastically having velocity $v$ with a wall, then it retraces itself with the same velocity. Impulse on the ball due to wall is $2mv$ and since there is no external ...
2
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1
answer
84
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Do the balls keep moving forever?
In a hypothetical world where there is no friction, and all collisions are elastic would an object in lateral motion be perpetually moving and never come to a stop?
Assumptions:
Perfect vacuum: zero ...
- 123
1
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0
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259
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Colliding elastically in lab and CM frame
Two spherical bodies of mass $m_1$ and $m_2$ are placed in gravity free space as shown. Initially, the body with mass $m_2$ is at rest and the body with mass $m_1$ approaches the other body with a ...
- 412
2
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2
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1k
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Are these collisions equivalent?
Similar to the question if two cars with a velocity of 50 mph each colliding is the same as one car colliding with wall at 100 mph, I was wondering if the same amount of energy is produced when ...
- 23
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1
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69
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Analysis of collision of a non-pivoted rod with a ball at one end?
Suppose a a unpivoted rod in free space is struck by a ball at one end and we know the initial condition what will be the outcome of the collision?
1
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2
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528
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A rubber ball hits a stationary door and bounces back, while a another ball sticks. Why doesn't the rubber ball violate conservation of energy? [duplicate]
According to the conservation of momentum and kinetic energy, in a perfectly elastic collision,
$m_{1i}v_{1i}+m_{2i}v_{2i}=m_{1f}v_{1f}+m_{2f}v_{2f}$
$ \frac{1}2 m_{1i}v_{1i}^2 + \frac{1}2 m_{2i}v_{...
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2
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1k
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About collision between an electron and photon
Can the collision between an electron and photon be inelastic? How about the energy loss in the collision as binding energy and photon bond with the electron due to high-energy collisions?
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5
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358
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If a car collides with an immovable, unbreakable wall, does energy lost or force determine damage? [duplicate]
$KE = \frac{1}{2}mv^2$ meaning the KE lost on impact would increase quadratically with speed, but f = ma would mean that force the wall applies to the car increases linearly with speed. So which ...
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1
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338
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Inertial vs Non-Inertial Reference Frame
Suppose a hypothetical universe is created with only two objects in it, A and B, of equal mass M, separated by some distance and initially stationary relative to each other. Of course at this point ...
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1
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934
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Question about 3d collision of 2 particles [duplicate]
I'm wondering about how to calculate the resultant velocity vectors of an elastic collision of two particles of same mass, in 3d. I've seen a post on the subject in which you answered, but I didn't ...
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1
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768
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Problem conserving 4-momentum at CoM frame in an inelastic collision [closed]
I am confused about the case where mass is not conserved in a collision (not due to relativistic factors). The center of momentum (CoM) frame is not the same before and after the collision.
Let's ...
- 123
5
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1
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16k
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Collisions between an object and a wall
Is momentum conserved when an object bounces back against a wall? The wall doesn’t move, but the object moves in the opposite direction. Assume this is an ideal, elastic collision.
If, initially, the ...
- 1,499
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1
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Proving the conservation of 4-momentum for a particle collision $A+B\to C+D$
Let me say that particle A hits particle B and two particles come out - C and D;
In system S I can write: $$p_A^μ+p_B^μ=p_C^μ+p_D^μ;\tag{1}$$ here $p_N^μ$ is the 4-momentum.
Using the Lorentz ...
- 125
1
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1
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4k
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Elastic Collisions and Relative Velocities
In a 1D elastic collision, it is well-known that the relative velocities of the two objects (before and after the collision) are reversed. What is the extension of this result to 2D or higher? Is ...
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4
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3
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3k
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Determine resultant velocity of an elastic particle-particle collision in 3d space
So I have two particles that have collided in 3 dimensional space. I want the particles to rebound off of each other in an elastic manner. How do I determine the resultant velocity vector if I know: ...
- 51
8
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5
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25k
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Why is momentum conserved when a ball hits a vertical wall?
Almost in every book on physics, there's an example of conservation of momentum when the ball that is moving horizontally in the air, hits some massive wall. They claim that the return speed of the ...
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