need physics lesson

[remo]

This is off topic of martial arts, but an important question for me, so I put it here.

All of you physics majors,

My understanding of energy transfer is woefully inadequate, as can be seen from some of my posts. :rolleyes: So, I need help in getting the basics down.

Question:
Two cars, one going 100 mph, the other 200 mph.(I know, crude and rudimentary, sort of like me :cool: )
Both hit the imaginary brick wall.
Aside from the death and destruction, not to mention the hefty insurance hikes, how much harder will the 200 mph car hit the wall?
Only twice as hard?
How much more energy will it take to push the second car twice as fast as the first?

I realize this is simpleton stuff, but I have gotten off on the wrong track somewhere and I need to get back on. (I’ve fallen down and can’t get back up) :eek:

I only ask that you answer in english, I won’t get the quantum physics thing.
Thanks in advance. :)

[kungfu cowboy]

Do the cars start from any particular speed from any particular distance? Is it an elastic or inelastic collision? Any more info?

E Pluribus Rectum

[Braden]

how much harder will the 200 mph car hit the wall?

4x as hard, assuming equal masses.

How much more energy will it take to push the second car twice as fast as the first?

Not enough information.

[remo]

Kungfu cowboy, Braden,

I'm trying for a solid brick wall, dead stop. (pun)

You've already gone past me with the starting of the cars, I was thinking they're 'in motion'?
(Make any sense?)

Thanks for replying. :)

[kungfu cowboy]

Yeah, were you given the mass of each car? That would be just grand!

E Pluribus Rectum

[kungfu cowboy]

Ahhhhhhh, they DON'T stop, because it's an IMAGINARY wall, right?

E Pluribus Rectum

[remo]

I'd like to see a couple of Buicks do the smash up! :)

For simplicity, both would be the same.

You'll have to guess on the weight of a Buick.

:D

"We forge our bodies in
the fire of our will." Han
from 'Enter the Dragon'

[kungfu cowboy]

Is there a gaggle of drunk teens driving? Their weight must be included also.

E Pluribus Rectum

[honorisc]

If I had kept at it years ago I could be so much further now, Humorous meloncholly of the Self.

You are thinking Fast.

How does Faster work...try these concepts:

faster=more force of impact

Weight of cars influences force of impact

force=mass x velocity

A 500 pound car traveling 200 mph then hitting a wall might not hit the wall with the same force as an eightteen wheeler hitting the wall at 100 mph.

The same weight? 2 tons x 100 mph = 200 something or others

2 tons x 200 mph = 400 something or others

2 tons x 300 mph = 600 something or others

2 tons x 25 mph = 50 something or others.

differing weight

1 ton x 200 mph = 200 something or others

1/2 ton x 200 mph = 100 something or others

1/4 ton x 200 mph = 50 something or others

Now, the wall...

A wall a mile thick will get damaged differently that a wall six inches thick.

A wall of bricks will get damaged differently than a wall of steel, or a wall of feathers or a wall of foam.

Some would get dented. Some would break differently.

Also how wide the wall...
a wall only as big as the vehicle gets obliterated depending on the force of impact and the make-up (density~) of the vehicle. Awall a mile long might get a break in the wall, but still stand, yet get knocked down if the vehicle is going slow enough...You can put a hole in a paper towel with whipping speed without really disturbing the rest of the towel. If you go slow enough you can affect the whole towel. Also if the towel is wet or dry matters with the area of force(pin head size, fingertip size, fist nuckles size, palm heel size,knee size...)...

force depends on how heavy~ and how fast.

Damage depends on what material both are made of, how sturdy is the standing object(object to be hit) and the force og the object doing the hitting~.

Very some such,perhaps might have been, likely say some, some not.

[remo]

No-Know,

Yes, I know what you mean.

Have you seen the swung axe buried into the stump of tree trunk setting on a bunch of inverted paper cups?

Or, more closer to this forum, the sledge hammer swung down onto the stack of cement slabs supported by the martial arts student/instructor, usually suspended between two chairs at his/her head and feet?

With all these tricks and variables, do you think it is possible to truly measure the impact and effectiveness of a punch or kick with an external device? (something mechanical, without actually smacking some poor test fool upside the head)

[Braden]

F = ma NOT F = mv

He's more interested in the kinetic energy equation though. Which is where I got my answer from.

[JerryLove]

F=MA^2 describes accelleration / decelleration.

Assume both cars are the same weight (2 tons) so we can just leave mass at M as it's constant. We are computing force. So what is the A?

That would be the speed change (either 100 to 0 or 200 to 0) over the time it took to get the speed change.

The stop is never "instant". If it were, force is infinate. Feel free to plug in the numbers you see fit, force in this instance will be in poundseconds.

The simpler F=MV describes potential energy in a given moving object. M is constant, so if we simplify 100mph and 200mph as V and V*2, we find that F=MV and F=2MV so the potential force doubles.

This all varies on what you are trying to measure. But remember (EVERYONE FORGETS THIS) that when measuring F-MA^2, IT HAS NOTHING TO DO WITH THE ACCELLERATION RATE ON THE CAR COMING UP TO SPEED!!!. It has to do with the *decelleration* rate at impact.

[davy]

Please stop:

in terms of simple energetic consideration, you should use the simple formula:

Kinetic Energy = 1/2 * Weight * speed * speed

(using this formula, you assume that you consider the cars as the same as a point having the weight of the car)


ANd please, no : "same weight, twice faster, so twice the impact"....

[JerryLove]

Oh, one of those "Here's my 2 cents, now no one repond" posts?

[Braden]

If you'll check, Davy, I used that equation in the second reply to this thread.