Many pupils think that the law of conservation of momentum in collisions applies only to situations in which one or more objects is visibly moving after the collision.
Misconception
Pupils may struggle to apply the principle to situations where one object does not appear to move, such as a snowball colliding with a wall.
Resources that Address This

Investigating momentum during collisions (1116)
Source  Practical physics/ Force and motion/ Momentum
A moving glider on a linear air track collides with a stationary glider, thus giving it some momentum. This datalogging experiment explores the relationship between the momentum of the initially moving glider, and the momentum of both gliders after the collision.
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Episode 220: Momentum and its conservation (1619)
Source  TAP/ Mechanics/ Momentum
This episode introduces the concept of momentum and its conservation  using a number of different examples.
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References
The following studies have documented this misconception:
 Clement, J. () "Students' alternative conceptions in mechanics: a coherent system of preconceptions?" In H. Helm, and J. D. Novak (Eds.), Proceedings of the International Seminar: Misconceptions in Science and Mathematics. Cornell University, Ithaca, NY.
310315.