The a 400 kg spacecraft has a momentum of 30,000 kg·m/s up. what is the velocity? a. 12,000,000 m/s b. 1200 m/s c. 300 m/s d. 75 m/smass of a baseball stays constant. as the velocity of the ball increases, what happens to the momentum of the ball?

Momentum of an object is calculated by multiplying the mass by the velocity. 

p = mv 
where:
p = momentum
m = mass
v = velocity

Let's take your given into account and put it in the equation:

p = mv
30,000 kg.m/s = (400kg)v

Velocity is our unknown, so to get it all we need to do is transfer mass (m) to the other side of the equation and isolate the velocity (v). When we do this, we need to use the opposite operation (rules of transposition). 

(30,000kg.m/s)/(400kg) = v

Cancel out the kg and you are left with m/s.

75m/s = v

The answer is then D. 75 m/s.

Now for your second question, as you can see in the formula, mass and velocity is directly proportional to momentum. That means that the higher the mass or the velocity, the higher the momentum.

So if the velocity increases, the momentum increases as well.