In physics lab we collided two objects that then both started moving in the same direction. We measured the velocities through two photo gates. We know momentum was lost because the velocities decreased after the collision. What are two physical reasons for the loss of momentum?
Note: In collision momentum is not lost, there is only loss of energy.
Again you can say loss of mechanical energy, because, the mechanical ...
The question is answered succinctly in approximately 100 words.