Final answer:
Momentum is affected by mass and velocity, and when mass is constant, momentum is proportional to velocity. In a collision without external forces, momentum is conserved.
Step-by-step explanation:
Momentum is affected by two factors: mass and velocity. This means that momentum is the product of an object's mass and its velocity, which includes both the speed and direction of motion. If an object's mass is kept constant, its momentum is directly proportional to its velocity. In the context of a collision where there are no external forces, such as the collision between two objects of equal mass where one object is initially moving and the other is at rest, the conservation of momentum applies. In this scenario, momentum is conserved, but kinetic energy is not necessarily conserved because some kinetic energy might be converted to other forms of energy during an inelastic collision.