Question

I have a middle school physical science worksheet here that is dealing with momentum. I believe there is a mistake in the wording of the question: "A 160-kg lineman picks up a fumble and heads toward the goal line. He hits another player to make a touchdown. The player he hits is moving at 4 meters /sec. What is the lineman's momentum?" -- My question is, it seems odd the way it is written. Is the player HE HITS moving at 4m/s before or after impact? Do we need to know the player HE HITS mass in order to calculate the conservation of momentum?

Answer 1

Yes, i'm going to say that the player he hits is already moving at 4m/s. However, even though my momentum physics is a bit rusty, I'm fairly sure you need more information. Good pick up though

Answer 2

You definitely need more information here. (There are apparently 5 NFL players who
weigh in at >160 kg, so you could assume equal masses.....)

Answer 3

I *think* the worksheet either wished to state that the LINEMAN was moving at 4m/s, and thus we could calculate the lineman's momentum, or it failed to mention the defensive player's mass, which would at least allow us to calculate the lineman's momentum given the law of conservation of momentum. However, this question also fails to specifically address whether or not the defensive player was moving at a velocity of 4m/s BEFORE or AFTER impact, which makes a big difference. Just a bad question and I should throw it out? Or can I add the defensive player's mass on my own to the question? I just wanted to double check that I was not missing something from the question.

Answer 4

In order for this question to make sense, you need to make assumptions about
the first line man's speed before the collision, the second linemans velocity
before and after the collision, and the mass of the second lineman.

In order to use conservation of momentum, you need the momentum of both players before the collision, and you need to know something about what happened after.