Re: Relative velocity problem....

[George Spagna <gspagna@rmc.edu>]

At 09:21 PM 9/10/97 -0400, you wrote:
> Please help me get a concept across to my students.  Here is the problem:
>
> A person rides in the back of a pick-up truck moving forward at +20 mph
> (relative to ground).  The person throws a brick toward the back of the
> truck at -5 mph (relative to the truck).  What is the resultant velocity of
> the brick relatvive to the ground?
>
> I know that the brick will move forward at + 15 mph relative to the ground.
> My students can't really believe this.  Oh, they will accept it simply
> because I told them that is what happens, but they do not really believe
> that you can throw something backwards yet have it really be moving
> foreward relative to the ground.  I have no modeling software (i.e.
> Interactive Physics) at the moment.  And short of going to the parking lot
> with a truck and a brick (maybe basketball -- safer) I am at a loss getting
> them to believe this.

Actually, this is the _best_ solution!  The mantra for teaching physics
ought to be "Experiment, experiment, experiment" rather than "Software,
software, software" !  :)


George Spagna           **********************************************
Department of Physics   * "Spoon-feeding, no matter how attractive   *
Randolph-Macon College  *    at 1300 hours on a Friday afternoon,    *
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phone: (804) 752-7344   *          - Elizabeth Timoney (1994)        *
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e-mail: gspagna@rmc.edu **********************************************
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