Q:  The inset in the figure above shows the
      solar system.  Assume that the little oval
      is about 40 AU in radius.  Recall that
      1 AU = 150 million km.

      Look at the blob of material to the left
      of the main disk.  Estimate its velocity in
      km/sec.  Compare it to a speeding bullet,
      which moves at less than 1 km/sec.


         The blob moves very roughly 20 AU
         over the course of about 1 year.
         That means it covers

                          distance
            speed  =   --------------
                           time


                        20 * (150 million km)
            speed  =   ----------------------
                          365 * 24 * 3600 s


                   =   approx  100 km/s