Assume that one object collides with a second object that is at rest. In which of the following scenarios would you expect that momentum would not be conserved?
a) When both objects move in the direction of initial motion after colliding.
b) When the objects move in opposite directions after colliding (the second object moves in the direction of initial motion, the first object moves in the reverse direction).
c) When the objects stick together after colliding.
d) When there is an external force (like friction) acting on the objects in the system.
