Afreight train rolls along a track with considerable momentum. if it rolls at the same speed but hastwice as much mass, its momentum is
a. zero. b. doubled. c. quadrupled. d. unchanged.

Two steel balls, each of mass m, are welded to a light rod of length l and negligible mass and are initially at rest on a smooth horizontal surface. a horizontal force of magnitude f is suddenly applied to the rod as shown. determine (a) the instantaneous acceleration a of the mass center g and (b) the corresponding rate at which the angular velocity of the assembly about g is changing with time.