Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: wheels come off - speed doubles?



When a small object, like a car tire standing in the road, is hit by a
large object, like a 57 Chevy Truck (back when trucks and bumpers were
both steel) and the collision is elastic, conservation of momentum
and energy require the small object will go forward with approximately
twice the velocity of the large object. This result is independent
of the speed of the large object, as long as the collision is elasitic.
I can see this being given as a rule of thumb in an introductory
physics class. The policemen probably remembered the rule, but forgot
the thumb. My students do it all the time.
The rule does not apply if an object simply falls off a truck.

If an object being carried by a truck, gets loose and under perfect
conditions collides with the truck (for example, hitting the tailgate),
it can be projected forward with twice the speed of the truck.
It is not likely that wheels coming off a truck would satisfy these conditions,
but it is possible. To get double the speed, it is more likely that the
wheels were hit by a second truck, but there
is no mention of a second vehicle in the article.



For those who missed the truck tire article, I happened to have looked at
it and it was still in my browser window....


North Carolina Highway Patrol troopers are looking for a truck driver who
lost two large tires Wednesday.

The tires are wedged into the wall of Sampson County home, destroying the
bedroom they flew into.
Newton Grove police believe the truck was speeding, possible going 55 in
a 35 mph zone,
when the extra wheels came off a trailer, barreling into the house at 110
miles per hour.

"As they come off, it doubles in speed," said Officer John Wilson of the
Newton Grove Police Department.
"The tires had come off the trailer, through a field, over a road,
through the yard and into the residence."

No one was inside at the time, however a relative watched from
the garden.

The truck did not stop.

Troopers are using numbers on the tires to find the driver, who they said
will be charged with hit and run.




--
________

FORTRAN is not the answer; FORTRAN is the question. The answer is "No!"
________

Floyd James North Carolina A & T State University
fjames@unicorn.ncat.edu