A 4 kg dog stands on one end of a 20 kg boat. The dog is initially 6 m from the shore, but then walks along the boat 2 m towards the shore. Answer the following questions assuming that there is no friction between the boat and the water:
a) How far has the center-of-mass of the "dog-boat system" moved after the dog has walked the 2m?
b) How far has the boat moved after the dog has walked the 2m ?