Re: Work-energy worries

[Herbert H Gottlieb <herbgottlieb@JUNO.COM>]

On Mon, 07 Oct 2002 12:11:38 -0500 "Lemmerhirt, Fred"
<FLemmerhirt@WAUBONSEE.EDU> writes:
> I am about to assign the this problem:
>
> A 75kg boater tosses a 5kg anchor horizontally, straight forward
> across the bow of his 125kg boat at 2m/s relative to the water.
a) Neglecting any  horizontal force applied to the boat by the water,
   calculate the boat's backward speed across the water just as the
   anchor leaves the boater's hand.
> (The boat is initially at rest on the water.)

b) At least how much work  must the boater have done to throw
    the anchor in this way?
>
*** The problem appears to be a conventional problem involving
       conservation of momentum to solve part a)  and conservation
        of kinetic energy to solve part b)

        However, because the friction between the boat and the
        water is substantial, the problem is unrealistic and would be
impossible
        to solve without much more information.  Why not choose
        a more realistic problem that involves the same concepts?
        For example, remember the one about the astronaut who
        was working outside the space station when her tether line
        broke and she had to throw away her $10,000 battery-operated
        wrench to get back to the space station.

Herb Gottlieb from New York City
(Where it is impossible to ignore the water friction on a 125 Kg boat
when
the 5 Kg anchor is thrown overboard.)

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.