A Cars forum. AutoBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » AutoBanter forum » Auto newsgroups » Driving
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

A Physics Question



 
 
Thread Tools Display Modes
  #1  
Old September 8th 06, 04:15 AM posted to rec.autos.driving
Alan Baker
external usenet poster
 
Posts: 2,026
Default A Physics Question

In article >,
Scott en Aztl?n > wrote:

> Imagine there is a 4-door sedan, such as a Honda Accord, parked on an
> asphalt surface. In your estimation, how fast would a compact pickup
> truck, such as a Ford Ranger, have to be travelling in order to strike
> the Accord and move it SIDEWAYS (i.e. perpendicular to the direction
> the wheels normally roll) by 15-18 inches? Imagine that the point of
> contact betwen the two vehicles is the truck's bumper and the rear
> quarter panel of the car.
>
> Follow-up question: how much damage would you expect to see on the two
> vehicles?
>
> Thank you for your insight.


This really isn't that hard a question.

Assuming that the sedan's tires are the only ones providing the braking
force then the question devolves to how fast the two vehicles can be
moving at the instant after impact and be stopped in 18 inches.

Since the combined masses of the vehicles will be roughly doubled, the
maximum deceleration of the tires will be roughly halved.

Final speed squared = initial speed squared + 2 acceleration * distance

vf^2 = vi^2 + 2ad.

a = 0.5g = 16ft/sec^2

d = 1.5ft

vf = 0

Solve for vi:

vi = (2ad)^(1/2)

= 48^(1/2)
= 6.9 ft/sec = 4.7 mph.

But that is the speed of the two moving *after* collision. If they weigh
roughly the same, then the truck will be moving roughly twice as fast
before impact.

10 mph.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling four feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect if you
sit in the bottom of that cupboard."
Ads
  #2  
Old September 9th 06, 05:49 AM posted to rec.autos.driving
Alan Baker
external usenet poster
 
Posts: 2,026
Default A Physics Question

In article >,
Scott en Aztl?n > wrote:

> Alan Baker > said in rec.autos.driving:
>
> >Assuming that the sedan's tires are the only ones providing the braking
> >force then the question devolves to how fast the two vehicles can be
> >moving at the instant after impact and be stopped in 18 inches.
> >
> >Since the combined masses of the vehicles will be roughly doubled, the
> >maximum deceleration of the tires will be roughly halved.
> >
> >Final speed squared = initial speed squared + 2 acceleration * distance
> >
> >vf^2 = vi^2 + 2ad.
> >
> >a = 0.5g = 16ft/sec^2

>
> Pardon me for asking, but how did you determine that the acceleration
> is 0.5g? Are you making some assumptions about the coefficient of
> sliding friction of the sedan's tires?


I was somewhat generous in the figure. Rubber on asphalt can approach 1g
when loaded with the entire mass it must accelerate, so when it must
decelerate twice the mass from which it receiving downward load (i.e.
when one vehicles tires are stopping both that vehicle and another of
equal mass) the deceleration will be half that value. But since sliding
friction is actually a little less than non-sliding friction, you may
redo the math if you wish.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling four feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect if you
sit in the bottom of that cupboard."
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Race Car Physics Question: FWD vs. RWD phaeton Technology 14 September 12th 06 02:52 PM
2005 Mustang Fog Light Question Craig Shaffer Ford Mustang 2 June 23rd 06 06:24 PM
1993 Saturn Fuel Filter Question OHC (SOHC)? [email protected] Saturn 7 May 21st 06 08:39 PM
GTP High Framerates=neutered physics TY Simulators 6 January 26th 05 09:38 PM
009 Distributor question [email protected] VW air cooled 5 December 31st 04 10:52 AM


All times are GMT +1. The time now is 02:52 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AutoBanter.
The comments are property of their posters.