Joe slides along an icy sidewalk -- easy version
Joe, whose mass is 50 kg, 
slides along a perfectly frictionless icy
sidewalk at v = 5 m/s.
However, he hits a patch where some sand adds
friction.
The patch has a coefficient of kinetic friction
of mu = 0.10, and the patch is L = 3 m wide.
-  What is the friction force on Joe when he
        is 1 meter into the patch?
 -  What is the friction force on Joe when he
        is 2 meters into the patch?
 -  Draw a graph showing "Net Force on Joe" 
        as a function of "distance along patch".
 -  What is the work done by friction as Joe moves
        across the patch?
 -  What is Joe's final speed?