If you were in a car that drove off the edge of a cliff, why would you be momentarily weightless? would gravity still be acting on you?

Gravity will be on you since you are falling. For instance if you where skydiving you are free falling which will be similar to the car. Therefore gravity does play a role because whatever goes up must come down.

Explanation:

moving ball hits still ball. mover stops, hit ball moves. momentum transfer.

conservation of mass

mass before something happens = mass afterwards