Astudent records the mass of a piece of iron the iron is then left outside until it rusts. what type of reaction occurs and how does the mass of the object after rusting compare with its original mass

Abumper car with a mass of 250 kg is traveling at a speed of 4 m/s. this bumper car collides and sticks to a second bumper car with a mass of 250 kg, which is initially at rest. what is the final speed of these two bumper cars after the collision, assuming they remain stuck together?