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Any ideas?

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- Thread starter poole_3
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- #1

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Any ideas?

- #2

marcusl

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To calculate the force, you need the acceleration. You can estimate this by assuming the acceleration (actually deceleration) is uniform and occurs in a time tau. It is complicated by safety features (crumple zone) in the auto that absorb and dissipate energy.

The following thread contais some details:

https://www.physicsforums.com/showthread.php?t=365317"

The following thread contais some details:

https://www.physicsforums.com/showthread.php?t=365317"

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- #3

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To calculate the force it would apply you'll have to know how long the car is impacting the wall for. You can estimate it if you don't have any other information, or calculate it somehow knowing certain properties of the materials of the car if you know that much. I, not having any other information, could estimate the impact to last lets say .2 seconds. Assuming the car impacts the wall to zero speed, the impulse will be equal to the moment it has.

p = mv

[tex]\Delta[/tex]p = F[tex]\Delta[/tex]t

and since final momentum is zero,

mv = F[tex]\Delta[/tex]t

or,

F = [tex]\stackrel{mv}{/Delta t}[/tex]

2300 lb's [tex]\approx[/tex] 1043 kg (mass of car)

40 mph [tex]\approx[/tex] 18 m/s (mps) (velocity of car)

We can just estimate [tex]\Delta[/tex]t to be .2 seconds duration, and you get F to be,

F = [tex]\stackrel{(1043 kg)(18 mps)}{(.2 s)}[/tex] = 93870 N = 21103 lb's

(I converted the weight of the car to the mass of the car in Kg and all other units to SI units, then converted final force back to lb's)

p = mv

[tex]\Delta[/tex]p = F[tex]\Delta[/tex]t

and since final momentum is zero,

mv = F[tex]\Delta[/tex]t

or,

F = [tex]\stackrel{mv}{/Delta t}[/tex]

2300 lb's [tex]\approx[/tex] 1043 kg (mass of car)

40 mph [tex]\approx[/tex] 18 m/s (mps) (velocity of car)

We can just estimate [tex]\Delta[/tex]t to be .2 seconds duration, and you get F to be,

F = [tex]\stackrel{(1043 kg)(18 mps)}{(.2 s)}[/tex] = 93870 N = 21103 lb's

(I converted the weight of the car to the mass of the car in Kg and all other units to SI units, then converted final force back to lb's)

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- #4

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Also, is .2 seconds a reasonable assumption for the time of this impact?

Thanks

- #5

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What is interesting in this puzzle is that two cars of equal mass hitting head-on will have the same impact as each one hitting a brick wall independently.

- #6

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- #7

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Without extensive FEA data on the two cars in question, there's no accurate way to model a collision. Simplest method is to carry out the actual collision with the demo cars loaded identically to the actual crashed ones, and videotape it for analysis.

- #8

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One problem i can forsee is that the cars will change directions aswell. I dont know if this affects my method i have stated above. I belive it does but im too tired to get my calculator and i just did this in my head ha ha.

Sincerely,

FoxCommander

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