Jack makes a pumpkin-powered momentum-mobile.

How fast will Jack be moving after he throws this single pumpkin to the right?

Now Jack starts from rest again, but this time he has two pumpkins.

Jack throws the first pumpkin to the left.

Then Jack throws the second pumpkin to the left.

How fast will Jack be moving after he throws both pumpkins to the left? Is this exactly twice as fast as before?