Taking the AP b and recently i did this lab on collision

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    Ap Collision Lab
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Homework Help Overview

The discussion revolves around a lab experiment on collisions conducted in an AP Physics B course. The original poster describes three types of collisions: one where a stationary car is hit, one where two cars collide head-on, and one where a car with a higher velocity hits a slower car. The poster is grappling with the classification of these collisions as elastic or inelastic based on experimental results and theoretical definitions.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to classify the collisions based on momentum and kinetic energy conservation, questioning the nature of the collisions when experimental results do not align with theoretical expectations. Some participants question the assumptions about the nature of collisions and the impact of external factors like friction on the results.

Discussion Status

Participants are actively engaging with the original poster's observations, providing insights into the definitions of elastic and inelastic collisions. There is recognition of the complexity involved in real-world experiments, and suggestions to reconsider experimental conditions are being discussed. No explicit consensus has been reached regarding the classification of the collisions.

Contextual Notes

There are indications of potential experimental errors, such as friction affecting momentum conservation. The original poster has not yet completed all parts of the experiment, particularly the third collision scenario, which may influence their conclusions.

victorlee2
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Homework Statement



well this is just a over all question. I am currently taking the AP b and recently i did this lab on collision. there were 3 collisions, a) one stationary while another one hits it b) both masses crash into each other c) both has velocity but one has higher velocity to collide with the lower velocity car. So far i did (a) and found that it is elastic collsion since both momentum and kinetic energy is conserved, however when i did (b) the kinetic energies were kinda off, but when i looked it up online, MANY SITES tell me that if 2 cars crash into each other, it is elastic. so idk what i shuld put for this



Homework Equations


m1v1^2/2 = m2v2^2/2

The Attempt at a Solution



^ all up there
 
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I'm not sure what you are saying here. Two cars colliding with each other can be elastic or inelastic. It does not depend upon whether one or both cars are moving but on what happens in the collision. Kinetic energy is conserved if and only if the collision is elastic. That's pretty much the definition of "elastic collision".
 


victorlee2 said:
MANY SITES tell me that if 2 cars crash into each other, it is elastic.
No idea where you got those sites from, but NO, that is not true at all. Elastic collisions in reality are really ideal cases. Believe your experimental results; after all your conclusion should follow from the results in a lab right?
 


wow that was fast lol. ok so for

a) One car is at rest and another car has velocity.

for this part i put collision is elastic because one of my trails came out showing that momentum and kinetic energy is conserved

b) Two cars crash into each other

for this part, i know that momentum has to be the same but my results show me other wise. and from my kinetic energy data results, it shows me that the kinetic energies arent the same, so would this still be an elastic or an inelastic?

and from my observation, the two cars DID recoil after they collided.

c) one car has small velocity while another car with a higher velocity hits it from the rear ( rear end collision )

didnt get up to here yet but i think it would be inelastic collision since both cars will still have velocity after collision?
 


victorlee2 said:
b) Two cars crash into each other

for this part, i know that momentum has to be the same but my results show me other wise. and from my kinetic energy data results, it shows me that the kinetic energies arent the same, so would this still be an elastic or an inelastic?

and from my observation, the two cars DID recoil after they collided.
That momentum is not conserved suggests friction being non-negligible in this particular experiment. However, since your first experiment managed to achieve COLM to a reasonable extent (ie negligible friction), then I would recommend that you repeat this particular experiment.
victorlee2 said:
c) one car has small velocity while another car with a higher velocity hits it from the rear ( rear end collision )

didnt get up to here yet but i think it would be inelastic collision since both cars will still have velocity after collision?
There is no "I think it would be inelastic". It can be (almost) elastic or inelastic depending on experimental conditions.
 

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