Conservation of Energy and Momentum in CollisionsSection 7.4 – 7.5

Conservation of Momentum

• How do we apply conservation of energy and momentum to one dimensional problems?

Conservation

• Momentum is conserved in all collisions

• Elastic Collisions: collisions where kinetic energy is conserved

• Inelastic Collisions:

Elastic Collisions in One Dimension

• Two objects colliding elastically

• Know masses and initial speeds

Elastic Collisions in One Dimension

• Momentum and kinetic energy are conserved

• mAvA + mBvB = mAvA’ + mBvB’

• Use ‘ to show final speeds

• Two unknowns!

Elastic Collisions

• Do some algebra (page 176, if you are interested)

• vA – vB = vA’ – vB’

Example

• A proton of mass 1.01 u traveling with a speed of 3.60 x 104 m/s has an elastic head-on collision with a helium nucleus. The helium nucleus has a mass of 4.00 u and is initially at rest. What are the velocities of the proton and helium nucleus after the collision?

• 1 u = 1 unified atomic mass unit = 3.6 x 10-27 kg, but we don’t need this

Homework

• Read Sections 7.4 and 7.5• Do Problems # 22 - 27, Page 189