Inelastic Collisions

• Review Impulse/Momentum• 3 cases

– Inelastic Collision– Elastic Collision– Indeterminate

• Inelastic Collision examples• Ballistic Pendulum• Other Inelastic examples

“Gravity” movie

• Newton’s Laws (conservation of momentum)

• 90 minute orbital time (different orbits?)

• CO2 fire extinguisher thruster

• Reentry (she’s going fast!)

Review – Impulse/Momentum

• Collisions

•

•

1 2

F12 = force on 1 due to 2

Conservation of Momentum

• Too many variables – 3 possibilities

– Inelastic – eliminate variable

– Elastic - generate 2nd equation

– Indeterminate - need more info

Inelastic Example 110,000 kg railroad car traveling at 24 m/s strikes a second 10,000 kg car at rest. They couple together, what is final speed?

• Conservation of momentum

• Inelastic

Inelastic Example 1 (cont)• Make the moving car 20,000 kg

• Make the stationary car 20,000 kg

Inelastic Example 1 (cont)What happened to the energy?

• Kinetic energy before

• Kinetic energy after

• Lost in heat

Inelastic Example 2Calculate the recoil velocity of 5 kg rifle that shoots a 0.02 kg bullet at 620 m/s.

• Conservation of momentum

• Inelastic collision in reverse.

in opposite direction

Ballistic Pendulum• Sequence

– Conservation momentum– Conservation of energy

• Solve Backwards!

• Step 1: Conservation momentum:

• Step 2: Conservation of energy:

• Combining:

Ballistic Pendulum Example• Example

• For h2

• For h2

• Combining

Example 1

• 1. Conservation momentum

• 2. Conservation energy

Example 2

• 2. Work-energy

• 1. Conservation of momentum

Inelastic car collision

• Work-energy

• Conservation of momentum