Mistake Master
Mistake Master · AP Physics C · Unit 4 · Topic 4.3 · Step-Through Animation
One Signed Sum That Refuses to Change
You'll learnthat a system's total momentum holds through a collision while kinetic energy need not.
A 3 kg cart buries itself in a parked 1 kg cart; a body at rest bursts into two. Two dramas, one boundary, one signed momentum total that reads exactly the same before and after — while a second ledger, kinetic energy, keeps its own separate books.
MOMENTUM LAB
Before you start
What you're looking at
A 3 kg cart rolling at +4 m/s toward a parked 1 kg cart on a frictionless track; they stick together.
The question
How fast does the stuck 4 kg pair move, and is kinetic energy conserved too?
Watch for
The two ledgers: the outlined momentum total holding steady while kinetic energy drops.
What the symbols mean
Pink = momentum ledger (signed bars plus TOTAL); blue = kinetic-energy ledger; red = thermal energy.
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