momentum conserved during inelastic collision?

[dadasolee]

When child/sled system collides with a log (inelastic collision), is momentum conserved?

The answer key to BR seems to make a contradiction, saying that during the collision momentum is conserved and KE not conserved, whereas once the log comes almost immediately to a full stop, neither momentum nor KE is conserved. What's going on?

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[loveoforganic]

Without any external forces (friction), momentum is always conserved.

 

[dadasolee]

There's friction in both cases, and log exerts an external force on both situations... so why is it then momentum is conserved in one case and not in the other...?

 

[ChemEngSoonMD]

They wouldn't call it "law of conservation of momentum and energy" if it only happened once in a while would they?