The momentum does not change because he is going the same speed just a different way.
On the change in potential energy
I think its 60. I think you would subtract 144-84 to get the mass of the vinegar molecule.
All you have to do is get the culmative effect of the forces by predicting the direction in which each object will move. Just write down what you know and put down questions for your teacher.
Answer:
moving slowly is the answer