# Homework Help: Collision experiment

1. Sep 2, 2015

### Drizzy

1. The problem statement, all variables and given/known data

Car 1 (500g) collides with car 2 (500g). The initial velocity of car 2 is 0. The cars stuck together after the collision.

I have to come to a conclusion about the results that i got.
2. Relevant equations

Kinetic energy before: 0,233

Kinetic energy after: 0,125

Delta kinetic energy: 0,108

3. The attempt at a solution

I also calculated delta Ek with an equation. (I will insert a picture)

So my conclution is that the energy that is "wasted" is half of the energy that we had in the biginning.

I did the same experiment but Car 1 had a mass of 700g and car 2 remained the same. delta kinetic energy was 0,112 which is almost the same as in the first one. So I guess that delta energy is the same no matter how much the cars wheigh. Is my assumption correct?

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2. Sep 2, 2015

### brainpushups

You have not stated your uncertainty at all. Such a generalization based on one experiment without uncertainty is unwarranted. Can you do some more tests?

To address your question: you can work out the energy loss during a completely elastic collision. Note that this depends on the frame of reference. If you analyze the collision from the center of mass frame you can work out the maximum energy loss.

3. Sep 2, 2015

### Drizzy

I'm sorry i didn't understand anything. I am not a native speaker. But no i cannot do more tests unfortunately. In my lab report i have written: "the lost energy is the same in both test but I need more tests to come to the conclusion that it remains the same even though the mass differs"

4. Sep 2, 2015

### Drizzy

Can anybody help me?

5. Sep 2, 2015

### insightful

Calculate delta KE for the second experiment and see if it agrees with your data.

6. Sep 2, 2015

### Drizzy

I did. the first test was 0,108 and delta Ek on the second test was 0,112 so is it right?

7. Sep 2, 2015

### insightful

Can't say without more data. What was the initial KE for the second test?

8. Sep 2, 2015

0.345

9. Sep 2, 2015

### insightful

And initial velocity of 700g car?

10. Sep 2, 2015

### Drizzy

0,962 was the initial velocity

it was a 753g car to be more specific

11. Sep 2, 2015

### insightful

And velocity of 735g and 200g cars after collision?

12. Sep 2, 2015

### Drizzy

Sorry i messed up the numbers...
This is test number 2:

Car 1
m = 0,753 kg
V0 = 0,962 m/s

Car 2 had the mass of 0,503 kg

Their total mass after the collision is 1,256kg

V1 = 0,613 m/s
V1 is their velocity after the collision

13. Sep 2, 2015

### insightful

What is the theoretical V1 (from conservation of momentum)?

14. Sep 2, 2015

### Drizzy

it should be 0,745

0,962^2 * 0,753/2 = v^2 * 1,256/2

15. Sep 2, 2015

### insightful

No. m1v1=m2v2

16. Sep 2, 2015

### Drizzy

right i forgot

it should be 0,5767

17. Sep 2, 2015

### insightful

With this V1, calculate theorectical final KE.

18. Sep 2, 2015

### Drizzy

it should be 0,209

19. Sep 2, 2015

### insightful

Right. And your experimental final KE?

20. Sep 2, 2015

### Drizzy

0,236

21. Sep 2, 2015

### insightful

Right. I would conclude that your experiment is not accurate enough to reach a conclusion on a pattern for delta KE.

You can now easily calculate delta KE for various masses and velocities and reach a theoretical conclusion.

22. Sep 2, 2015

### Drizzy

Thank you sosososososo much for helping me :)

23. Sep 2, 2015

### Drizzy

i did this on the first test and my theoretical final velocity should be 0,492 but Mine was 0,499

it is pretty close so what should i do with this one?

24. Sep 2, 2015

### insightful

Either redo it or discuss the problem with the result.

25. Sep 2, 2015

### Drizzy

i cant redo it :( my friend told me that they got delta Ek to 0,206 and 0,208 so I suppose that delta Ek should remain the same... but something was defintly wrong with my velocity cuz the momentum has to be the same but it wasnt