Two trains start a journey at the same time 120 miles apart, travelling towards each other. the first train is travelling at 60 mph and the second train is travelling at 40 mph. how long does it take for the two trains to meet?

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.