If you double the velocity of a moving object, how is it's momentum affected?

Well momentum is = to Mass*Velocity so let's use an example to figure this out

If I weighed 50kg and I was jogging at 3m/s then I broke into a run at 6m/s how will me momentum be affected?

3m/s*50kg=150

6m/s*50kg=300

So as you can see by doubling the velocity you also double the momentum