Sc (21) , Y (39) , La (57) , Ce (58) , Pr (59) , Nd (60) , Pm (61) , Sm (62) , Eu (63) , Gd (64) , Tb (65) , etc (hoped that helped)
Answer:
Other than the fact that momentum is a "vector" quantity I wouldn't know.
If the car had a momentum opposite to the chosen positive direction then its total momentum would be negative.
That first one you have selected (3,-3) works in both equations so it's correct.
good job.
you can do this guess and test method with multiple choice answers. If it works in both equations it is the solution. Otherwise use substitution or elimination to combine the two into one equation in only one variable. Then you can solve for the one variable first and use it to solve for the other.
