Q:  What speed u will cause the rod to come
           to a complete stop?


         The angular momentum of the rod-plus-one-putty
         is 2.88 kg*m^2/s, out of the page.  In order for
         the collision to lead to zero final angular velocity,
         the angular momentum of the second wad of putty
         around the pin must be

               L (second wad)  =  2.88 kg*m^2/s      into page

                               =  m * u * (L/2)

                                2.88 kg*m^2/s
            -->       u   =  -------------------  
                              (0.4 kg) * (0.6 m)

                          =     12 m/s