This is simpler to calculate than you might assume - you need only find the velocity after one half life and double it. Doing that gives you 15.4 km/s. Of cou

This is simpler to calculate than you might assume - you need only find the velocity after one half life and double it. Doing that gives you 15.4 km/s. Of course this is considering only the decay of the plutonium and none of the active decay products. I've also disregarded the decrease in mass over time.