Estimate the initial velocity of the cars after the collision

  • #26
kuruman
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So far so good. There are two options left both of which are lower than the known speed of the car. Any ideas about eliminating either one of them?
 
  • #27
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So far so good. There are two options left both of which are lower than the known speed of the car. Any ideas about eliminating either one of them?
My first reason was that they should not be too different. Because they both have the same velocity relative to the ground before the cars collide. But the car velocity immediately goes to zero after the collision. The piece also slows down immediately. Because its velocity was the same as the car. But as I said in the previous reason, some of the energy released in this collision is spent on this piece. Of course, as I said, I do not think that this energy is so much that it can accelerate the piece a lot. I think the most appropriate velocity is the first option.
 
  • #28
kuruman
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My first reason was that they should not be too different.
What are "they" that should not be different? The speeds of the piece and car or the remaining choices (A) and (B)?
Because they both have the same velocity relative to the ground before the cars collide. But the car velocity immediately goes to zero after the collision. The piece also slows down immediately.
What do you think slows the piece down? Does whatever that is act on the piece as it flies through the air?
Because its velocity was the same as the car. But as I said in the previous reason, some of the energy released in this collision is spent on this piece. Of course, as I said, I do not think that this energy is so much that it can accelerate the piece a lot. I think the most appropriate velocity is the first option.
Suppose you said to an experienced accident investigator that the speed of the car before the collision was 2 m/s and he said to you, "The evidence on the ground does not support this", what do you think he saw?
 
  • #29
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What are "they" that should not be different? The speeds of the piece and car or the remaining choices (A) and (B)?
The speeds of the piece and car. Of course I'm not sure.
What do you think slows the piece down? Does whatever that is act on the piece as it flies through the air?
I do not know the reason. Because the car stops after the collision and on the other hand the piece is with it, so I thought the speed of the piece would also decrease.
Suppose you said to an experienced accident investigator that the speed of the car before the collision was 2 m/s and he said to you, "The evidence on the ground does not support this", what do you think he saw?
I think he saw pieces of the car body scattered over a long distance. In fact, he saw that the range of those pieces was so high that the collision was most likely severe, so the speed of the car should not be that number.
 
  • #30
kuruman
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The speeds of the piece and car. Of course I'm not sure.
How can you not be sure that you meant the speeds of the piece and the car? You know what you meant, I don't that's why I asked.
I do not know the reason. Because the car stops after the collision and on the other hand the piece is with it, so I thought the speed of the piece would also decrease.
"I do not know the reason" is not sufficient explanation when you claim something to be true. Consider a possible specific piece, a baby seat (without a baby) next to the driver's seat in a convertible with the top down. When the car collides and stops, the baby seat will stay in place or fly off depending on whether it is strapped in or not. Just because the car stops does not mean that the baby seat will have to stop. There is a reason why it stops. The fact that the baby seat was found on the ground farther away than the car indicates that it did not stop like the car but flew through the air and was stopped by the ground. That's the motion that we want to analyze, namely reconstruct the motion of the baby seat through the air.
I think he saw pieces of the car body scattered over a long distance. In fact, he saw that the range of those pieces was so high that the collision was most likely severe, so the speed of the car should not be that number.
The speed of the car should not be what number? You did not mention any numbers. It seems that you are linking the position of the pieces with the "severity" of the collision. How does one measure this severity? Did you really mean to say "the speed of the car before the collision must have been very high for the baby seat to land where it did"?
 

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