Kevin, Joe, and Nick are studying for their physics exam, but they are very confused about momentum conservation. A reading question in their text asks whether the momentum of a ball thrown upward is conserved after it leaves the hand. Kevin says, "The answer is yes since momentum is always conserved." Joe says, "It can't be. It slows down and speeds up." Nick says, "there's no other object involved after it's released so it must be conserved." Do you agree with any of them, or are they all wrong? Explain whether momentum is conserved for the ball and explain how you can tell in general whether the momentum of a system of objects is conserved. Note: This is an essay question. Your answer will be judged not solely on its correctness, but for its depth, coherence, and clarity.