Re: Car acceleration

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

On Fri, 1 Feb 2002, Herbert H Gottlieb wrote:

> I'm surprised at all of the incorrect answers that have
> already been given by listmembers to this question.  In
> my (not-so-humble) opinion, only choice A could be
> correct.

What?

> A. We are not told if the car engine is operating
> or if the road is level.  If the car accelerates
> forward on a down-sloping road it must be due
> to the component of the weight in the forward
> direction.

Oh, Herb, please.  We aren't told the color, make, or year of the
car either, but there is one thing you can bet your life on: Cars
do accelerate after stopping at intersections regardless of the
incline of the road itself and in almost every case the engine
*is* running.  Similalrly, in almost every case, when a car
accelerates along a level or upward inclined road, the only force
on the car that is in the direction of its motion is the
frictional force.  Do what (I hope) you tell your students: Draw a
free body diagram.

John Mallinckrodt      mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm