4.1.2.P16

Two students, Justin and Taylor, are discussing Newton’s third law, which says that when objects interact with each other they satisfy the following principle:

If object A exerts a force on object B, then object B exerts a force back on object A and the two forces are equal and opposite.

They are asked to consider four situations concerning two identical cars and a much heavier truck.

1. The two cars hit each other coming from opposite directions at equal speeds.
2. One car is parked and the other car crashes into it.
3. One car is parked and the truck crashes into it.
4. The truck is pushing the car because the car’s engine cannot start. They are speeding up.

Justin says, "It will only hold in the first case." Taylor says, "No, I think some of the other cases might also work." What do you think? Note: This is an essay question. Your answer will be judged not solely on its correctness, but for its depth, coherence, and clarity.

Joe Redish 10/2/13