Paceship 1 and spaceship 2 have equal masses of 300 kg. spaceship 1 has a speed of 0 m/s, and spaceship 2 has a speed of 4 m/s. what is the magnitude of their combined momentum?

Momentum is the product of an object's mass and its speed. Spaceship #1 is completely out of the running ... if it has no speed, then it has no momentum. Spaceship 2's momentum is (300 kg) x (4 m/s) = 1,200 kg-m/s, and that's the total momentum for both of them.

Now I have to ask you: How in the world do you measure their speed?

Or maybe I should ask: How OUT OF the world do you measure their speed?