Miata Mailing List: December 1995, Message #185
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   From: "Richard D. Buhl" 
Subject: Collision Closure Speed
   Date: Mon, 4 Dec 1995 13:56:46 -0500

A brief course in collision effects for the physics impaired.

>From Physics:
The law of conservation of momentum states that
M1*V1 + M2*V2 = MfVf
The law of conservation of mass (minus some turn signal glass)
M1+M2=Mf

So, if M1 = mass of Car 1 (miata) = 1000Kg (or about 2200lbs)
and M2 = M1 (miata vs miata)
then Mf = M1 + M2 = 1000 + 1000 = 2000kg

now if car 1 is going east at 50mph then V1 = 50 (east is positive)
and car 2 is going west at 50mph then V2 = -50 (west is negative)

then
M1*V1 + M2*V2 = MfVf
(50)*1000  + (-50)*1000 = 2000*Vf
then Vf=0

Therefore each car will decelerate from 50 mph to 0 mph.

Now if car 2 is a truck weighing in at 20 tons then M2 = app. 18000 Kg and
still going west at 50 mph then:
Mf=1000+18000= 19000
and
M1*V1 + M2*V2 = MfVf
(50)*1000 + (-50)*18000 = 19000*Vf
then Vf = -44.7

Which means that the speed after crash will be 44.7 mph going west.  This would
be equivilant (sort of) to car 1 (miata) hitting a brick wall at 94.7 mph.

Lets ban anything that wieghs more than a miata ;)

Tomorrow Jeannie will give me spelling lessons, and I will attempt to calculate
the decelaration and forces involved in the two crash cases.

Rick B.
STKR - Slower Traffic Keep Right
3 messages to the list in one day a new personal best :-O  <-loud mouth


-- 
Richard D. Buhl            Dikaia Upotheke          ferris@gts.elan.af.mil                      
Response to spelling/grammar complaints: 
   Damn it Jim I'm an Engineer not an English Teacher