Question

momentum and conservation

Answer 1

p1 = (1/2)m2*3 = 1.5(m2)
p2 = 2(m2)

Answer 2

Hmm okay, so your equations are set up correctly. And you have the momentum of each of the pucks. Now what is it about momentum and conversation?
How do these two terms relate?

Answer 3

idk, p=mv i guess

Answer 4

oh the final and initial momentum equals each other right

Answer 5

Well that's just the equation you used for the two pucks:) It's more of a concept question. What is it about momentum that is special? It has to do with the conservation part

Answer 6

the momentum before and after the collision is conserved

Answer 7

There you go!
In a closed system, the total momentum is conserved. So what we need first is the total initial momentum. We know the momentum for each puck, what is it as a total?

Answer 8

hey what is closed system

Answer 9

1.5 m2

Answer 10

It just means that no other forces or factors are affecting the pucks. It comes from physics more so... but back to what I said, how can we calculate the total momentum of each puck?

Answer 11

m*v = m1*3m/s

Answer 12

Well that's just for one puck, we want the ''total'' momentum, meaning all the momentum from both pucks. Think of it this way, if I have 3 apples and 5 apples , my total apples is 8. Or another way, you have two objects, one has a mass of ikg, and the other 3kg. Your total mass is 4kg from everything. It's the same concept, in that we just want the total momentum!

Answer 13

ohh 3.5m/s

Answer 14

What did you calculate at the start of this problem?

Answer 15

momentum of 2 pucks

Answer 16

There you go :) but not 3.5 m/s
We are dealing with momentum right now it would be 3.5 (m2)

Answer 17

no would n't it be -0.5 (m2) m/s as they both are in opposite direction

Answer 18

So that is our initial total momentum, now since momentum is conserved, the final momentum will also be 3.5 (m2)

Answer 19

Ah, you are right in that regards I didn't see the opposite direction part.

Answer 20

We can keep it positive for now, since we are not given any direction.

Answer 21

Now remember the momentum equation?

Answer 22

p=mv

Answer 23

Yes! :P
We are going to use that again. We know the momentum though, since it is conserved. Which is the 0.5 (m2)
The unknown we are looking for is the velocity. What about the mass though? What would be the mass, if the two pucks are stuck together now?

Answer 24

oh man...how to get that

Answer 25

Well what was the mass of each puck, separately?

Answer 26

1/2m2+m2=1.5m2

Answer 27

Good!

Answer 28

So that is our mass, so we have this....