
#1
Dec1812, 01:17 PM

P: 82

Hi,
I was wondering how one could know when velocity would be in the opposite direction in a momentum question. For example, two skaters are skating together (as one) at the same speed. Skater A pushes skater B and B moves at 13m/s. Find the speed of skater A. I found it and it's the correct answer. But I assumed skater A would still be moving in the same direction as opposed to the opposite direction (after pushing). So, logic?... 



#2
Dec1812, 01:44 PM

Mentor
P: 40,872

Recall that momentum is a vector. So if the direction of motion of skater A were reversed, his momentum would be different. Only one solution will conserve momentum.




#3
Dec1812, 01:54 PM

P: 82

True. But when is it reversed? How do I know when it is reversed?
Edit: Just based on the fact that momentum is conserved? In that case, how do I know when it's conserved? I assumed it always is. 



#4
Dec1812, 01:59 PM

Mentor
P: 40,872

Conservation of momentum theory question 



#5
Dec1812, 02:30 PM

P: 82





#6
Dec1812, 02:33 PM

Mentor
P: 40,872

That's all you need for this problem. Other problems may be more complicated and might require additional information. 



#7
Dec1812, 03:30 PM

P: 82

Lol, okay, thanks very much for your help :)



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