Question

At the instant a 2.0-kg particle has a velocity of 4.0 m/s in the positive x direction, a 3.0-kg particle has a velocity of 5.0 m/s in the positive y direction. What is the speed of the center of mass of the two-particle system?

Answer 1

find total momentum, the combined momentum is the same (no external forces) For example a man on one lassos the other and pulls them together. There was no external force, so momentum of combined mass is the same as the original two.
x direction:
2 * 4 = 8
y direction
3*5 = 15
total momentum = sqrt (64+225) = sqrt (289) = 17
so total mass of 5 kg is moving at speed s
5 s = 17
s = 17/5