Mutt and jeff are running along a path each pushing a cart loaded with rocks. if mutt's wagon has a mass two times greater than jeff's and they want to stay together, arriving at their destination at the same time, what must happen? a) jeff should slow down so mutt can catch up. b) mutt must use half as much force to push his cart. c) mutt must use twice as much force to push his cart. d) mutt and jeff will use the same force, but mutt will take bigger steps.

Force is directly proportional to mass according to the second law of Newton, meaning that the greater the mass is, bigger the force should be in order to move the object. In this case, Mutt's wagon has a mass two times greater than Jeff's and they have to be equal. So either Jeff must slow down twice as much or Mutt has to speed up twice as much. The only option we can choose  according to our reasoning is that Mutt must use twice as much force to push his cart, because his mass is two times bigger. According to me the answer is C).

their crystal patterns have been disrupted by stress

probably not if net force is zero