# “Classic” Collisions

Here are a few “famous” collisions whose outcomes are either obvious or can be calculated mentally.

(Perfectly) Elastic “Sitting Duck” Collisions

• For all the above,
• the total momentum is conserved.
• when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
• The two masses approach and separate from each other at relative speed of u.

Perfectly Inelastic “Sitting Duck” Collisions

• For all the above,
• the total momentum is conserved.
• when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
• The two masses travel at a common velocity after the collision.

(Perfectly) Elastic “Jousting” Collisions

• For all the above,
• the total momentum is conserved.
• when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
• The two masses approach and separate from each other at relative speed of 2u.

Perfectly Inelastic “Jousting” Collisions

• For all the above,
• the total momentum is conserved.
• when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
• The two masses travel at a common speed after the collision.