Which of the following shows an example of unbalanced forces acting on one or more objects? A- a person sitting still in a chair
B-two cards leaning against each other
C-one football player pushing another down to the ground
D-two football players pushing each other without either one of them moving

You are traveling in a car going at a constant speed of 100km/h down a long, straight highway. you pass another car going in the same direction which is traveling at a constant speed of 80km/h. as measured from your car's reference frame this other car is traveling at −20km/h. what is the acceleration of your car as measured from the other car's reference frame? what is the acceleration of the other car as measured from your car's reference frame?