# Linear Momentum (One Dimension) Quiz Question

1. Jul 15, 2010

### LeonGrande

Hello forum, today in my gr. 12 physics class I had a interesting question which I could not prove at all for the life of me. It is a really simple question, just with a little twist I suppose. As I was driving home from class I was thinking about what I was missing and thought up a solution. Anyways I'll state the question and all that jazz...

1. Two people are sitting in a canoe which sits in the middle of a lake. Both individuals have a mass of 75kg, and the canoe itself has a mass of 50kg. The canoe is not moving, nor are the people sitting inside. Person 1 decides to throw to Person 2 a life jacket (edit: life jacket has a mass of 1kg) at 10m/s [E].

Calculate the theoretical velocity of the canoe while the life jacket is still in mid air.

Also,

Calculate the velocity of the canoe after person 2 catches the life jacket.

Side note... the question was not worded at all like this, it was much more confusing! lol

2. Relevant equations

m1*v1o+m2*v2o=m1*v1f+m2*v2f

v=velocity
m=mass
o=initial, f=final

3. The attempt at a solution

So here is my attempt at a solution,

(a) (1kg)*(0m/s)+(200kg)*(0m/s)=(1kg)*(10m/s)+(200kg)*(X)
X= -0.05m/s

(b) (1kg)*(10m/s)+(200kg)*(-0.05m/s)=(1kg)*(0m/s)+(200kg)*(X)
X= 0m/s

...So there it is. I was not to sure whether or not I should have combined the masses or not.

Sorry for any typos, I just got home and am drained. Thanks for any help!

Last edited: Jul 15, 2010
2. Jul 15, 2010

### kuruman

Hi LeonGrande and welcome to PF.

Without the mass of the life jacket one cannot solve this. Looking at your solution, it is correct if the mass of the jacket is 1 kg. You seem to know what you're doing.

3. Jul 15, 2010

### LeonGrande

Yeah, sorry, the mass of the jacket is 1kg... >_>

Thanks for the quick reply! I guess I need to work on thinking clearly during tests/quizzes.

4. Jul 15, 2010

### kuruman

Then you are OK.