Object a has mass m and is traveling forward with speed v. which set of changes to object a will not affect its momentum?
mass reduced to 0.5m, speed increased to 2v

mass reduced to 0.25m, speed increased to 1.25v

mass increased to 2m, speed increased to 2v

the direction of velocity reversed, speed kept at v

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?