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## A Riddle…

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**A Riddle…**What do you get when you combine 2 bikes, two foam sticks and 2 idiots?**A Collision!**Conservation of Momentum**What does “conservation” mean?**The TOTAL AMOUNT OFMOMENTUM in a closed system WILL ALWAYS REMAIN CONSTANT pinitial = pfinal**Elastic Collision**Two objects collide and SEPARATE without any sticking Animation When the two objects have the same MASS, they TRADE MOMENTUM**Example #1**• A 2 kilogram ball moving at +3 meters per second collides with a 3 kilogram ball at rest. • Assuming that the 2 kilogram ball stops after the collision, calculate the velocity of the 3 kilogram ball after the collision.**Inelastic Collision**Two objects collide and STICK together Animation The MASSES of the objects COMBINE TO FORM A SINGLE MASS**Example #2**• A 5 kilogram cart moving right at 6 meters per second collides with a 10 kilogram cart moving left at 6 meters per second. • If the two carts stick together during the collision, determine their final velocity.**Explosion/Recoil**Two objects held together are PUSHED APART Animation Usually this system will BEGIN WITH A MOMENTUM OF ZERO**Example #3**• A 100 kilogram cannon has a 5 kilogram cannonball inside it. • When the cannonball is fired, what happens to the cannon? • If the cannonball has an initial velocity of 20 meters per second, calculate the velocity of the cannon. The cannon will move backward**SUMMARY**• Define the Law of Conservation of Momentum. • Why does the direction of an object’s motion matter? • Name and describe the three situations where momentum is conserved.