1. Conservation of momentum means: initial momentum = final momentum
m1v1i + m2v2i = m1v1f + m2v2f
If neither object is moving initially, then initial momentum = 0.
Ex: astronaut throwing oxygen tank
Objects collide and remain separate after the collision.
Ex: a moving billiard ball collides with a stationary . B.
equation simplifies to A.
equation simplifies to
m1v1i = m1v1f + m2v2f
0= m1v1f + m2v2f
If a moving object collides with a stationary one and they move as one.
Ex: a brick is dropped into a moving wagon.
Two moving objects collide and move as one.
Ex: two football players collide and move as one. C.
equation simplifies to D.
equation simplifies to
m1v1i = (m1 + m2)vf
m1v1i + m2v2i = (m1 + m2 )vf

2. Conservation of momentum means: initial momentum = final momentum
m1v1i + m2v2i = m1v1f + m2v2f
If neither object is moving initially, then initial momentum = 0.
Ex: astronaut throwing oxygen tank
One object moving initially. Objects collide and remain separate.
Ex: a moving billiard ball collides with a stationary ball . B.
equation simplifies to A.
equation simplifies to
If a moving object collides with a stationary one and they move as one.
Ex: a brick is dropped into a moving wagon.
Two moving objects collide and move as one.
Ex: two football players collide and move as one. C.
equation simplifies to D.
equation simplifies to