# Another physics problem

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• posted on November 25, 2004, 4:00 pm
I'm bored so will put forward this one to see what happens:
2 cars of equal mass crash head on at 50 mph. Both drivers will feel an impact equal to crashing into a solid object at: a. 100 mph b. 50 mph c. Other
Harry K
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• posted on November 25, 2004, 4:06 pm
c

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• posted on November 25, 2004, 4:14 pm
The answer is "A". 100 mph, because
E1β when two cars hit head on which means each car would absorb 50 kmh of kinetic energy BUT when a car hits a wall E1 is divided in 1/2, 1/2 going to the wall and 1/2 to the car. It's all in the wording of the question.

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• posted on November 25, 2004, 4:30 pm
wrote:

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• posted on November 25, 2004, 5:20 pm
On 25 Nov 2004 08:00:27 -0800, snipped-for-privacy@hotmail.com (Harry K) wrote:

50mph because ...........................................
2 cars of equal mass that crash head on at 50 mph can also be looked at as one car going 100mph crashing into a stationary car of the same mass.
When that happens the force of the collision at 100mph is cut in two and split equally between two cars.
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• posted on November 25, 2004, 5:44 pm

because of the theory of relativity, the colision will be slightly less than 100 mph.
randy
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• posted on November 26, 2004, 10:31 pm

I suggest you consult this site: http://britneyspears.ac/lasers.htm
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• posted on November 25, 2004, 5:47 pm

ps, if you hit a wall at 100mph, the wall absorbs some shock. but the effect is the same.
randy
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• posted on November 25, 2004, 5:24 pm
Let's see...
The driver in the car is going 50 miles per hour, hits the "other car", then suddenly stops going 50 miles per hour.
The driver in the car is going 50 miles per hour, hits the "solid object", then suddenly stops going 50 miles per hour.
In both cases, the driver is slammed into the seatbelt/airbag/dashboard at 50 miles per hour. Answer b!
"Harry K" wrote in message

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• posted on November 25, 2004, 5:27 pm
By the way, were the drivers OK after this crash? I hope they were wearing their seatbelts...
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• posted on November 25, 2004, 5:55 pm
Harry K wrote:

B. <yawn>
Bob
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• posted on November 25, 2004, 6:16 pm
another answer, neither driver will feel a thing...
randy

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• posted on November 25, 2004, 6:41 pm
Harry K wrote:

The correct answer is C and B
If both cars, and drivers were mirror images of each other and hit perfectly head on, it will be B, but since it is highly unlikely they will be perfectly matched, it will be C as the force will be slight unequal as some parts will not collide etc. But it will be close to B.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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• posted on November 25, 2004, 8:02 pm
You *are* bored.

Hmmm...is this a trick question? It's been a while....
Look at billard balls. When the cue ball strikes a stationary ball head-on (ignoring spin), the stationary ball beings moving and the cue ball stops dead. Let's say the cue ball was travelling at 50mph. Effectively it has hit a 'brick wall' at 50mph since it stopped dead. So if the second ball was travelling in the opposite direction at the same speed, the cue ball would not just stop, but 'bounce' and travel at 50mph in the oppposite direction. Effectively hitting a wall at 100mph.
Correct so far? Maybe, maybe not. At this point I don't care. :)
Now, that's all well and good but cars are a different story. Collisions are not perfectly elastic due to crumple zones and other losses. Assuming both cars 'stick' together after the collision, the wreck will remain stationary at the point of impact. In this case, each driver will feel the effect of hitting a wall at 50mph (i.e. each goes from 50mph to 0mph).
If the cars 'bounce' off each other, then the impact will be somewhere between 50 and 100mph.
Of course, dont forget about seat belts and air bags which may save their lives....if that gas leak didn't engulf the vehicles in flames first.
Do you actually have an answer to this 'problem'?
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• posted on November 25, 2004, 8:58 pm
Borrall Wonnell wrote:

Not really. The "brick wall" or more correctly an immovable object does not absorb any of the energy, it moves not at all. The stationary ball absorbs all the forward energy (ignoring losses) and uses this energy to move with. If the cue ball hits an immovable object it must absorb the energy itself, either bouncing off or flexing or breaking up.

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Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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• posted on November 25, 2004, 11:17 pm
Damn, and I just packed up my old college physic books for storage until my office gets renovation completed! I would have loved to look that one up, I can not remember most of my physics stuff, too long ago.
MC

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• posted on November 26, 2004, 12:58 am
Most of this energy is consumed in wadding up metal. That is the current design criteria.
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• posted on November 26, 2004, 2:48 am
dave snipped-for-privacy@hotmail.com (Borrall Wonnell) wrote in message

Yes, it is 50mph give or take allowing for crumple zones etc. I first saw this on in sophmore physics class in HS back in 1951. Quite a discussion and got into involved math etc but it all comes down to a simple mind excercise.
From what speed did each driver stop?? 50mph.
Harry K
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• posted on November 26, 2004, 3:49 pm

so the impact is the same whether you hit a wall, a 50mph car, or a 100000mph car.
i dont buy it.
randy
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• posted on November 26, 2004, 3:54 pm

although i may be overthinking it. seems inertia comes into play somewhere..
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