# Conservation of momentum for ball rolling up hill [duplicate]

I know that momentum is conserved in inelastic collisions. In other words, if the kinetic energy of the system is converted to potential, the momentum is still conserved

Suppose we have the situation where a ball is rolling up a hill. The ball does not have enough energy to get to the top of the hill, and so, it rolls back down.

The initial momentum was directed towards the hill, and the final momentum is directed away from the hill. How is momentum conserved?

• Effectively a duplicate of Collisions between an object and a wall. The hill is not a fixed object. The hill is attached to the planet Earth, and the whole planet moves (by a tiny amount!) so that momentum is conserved. – John Rennie Mar 8 '18 at 5:25
• This is just like when you drop a ball. How does it get all that momentum? Simple the earth moves a tiny amount upward. – SmarthBansal Mar 8 '18 at 6:00
• Possible duplicate of Collisions between an object and a wall – Chris Mar 9 '18 at 0:08