# A couple of questions

1. Oct 26, 2006

### TheHamburgler1

I have no idea how to do this first one

1. Youre coasting with a friend on a sled, going a constant velocity, having a momentum of +120kg m/s when suddenly your friend bails off the sled. Assuming there are no net external forces acting on the system which of the following gives a correct possibility for the final momenta for first your friend, then you and the sled?

a) -50 kg m/s, +170 kg m/s
b) -50 kg m/s, +120kg m/s
c) -50 kg m/s, -70 kg m/s
d) +70 kg m/s, -50 kg m/s
e) +120 kg m/s, -50 kg m/s

my other question: Is momentum conserved in both elastic and inelastic collisions or only elastic?

2. Oct 26, 2006

### arildno

Counter-question:
If a system is not experiencing any EXTERNAL forces, what can you say about the system's momentum?

3. Oct 26, 2006

### TheHamburgler1

It's constant right

4. Oct 26, 2006

### TheHamburgler1

This therefore means that the answer has to be B right? Because therefore the momentum for the sled is the same or am I wrong?

5. Oct 26, 2006

### arildno

What system is NOT experiencing external forces in this cases?

Is it:
i) You
ii) You+sled
iii) Sled
iv) Sled+friend
vii) Friend+you
viii) Friend
ix) You+Friend+Sled