1. Conservation of
Energy and
Momentum in
Collisions
Section 7.4 – 7.5

2. • How do we apply conservation of energy and
momentum to one dimensional problems?
Conservation of
Momentum

3. • Momentum is
conserved in all
collisions
• Elastic Collisions:
collisions where
kinetic energy is
conserved
• Inelastic Collisions:
Conservation

4. • Two objects colliding
elastically
• Know masses and
initial speeds
Elastic Collisions in One
Dimension

5. • Momentum and kinetic
energy are conserved
• mAvA + mBvB = mAvA’ + mBvB’
• Use ‘ to show final speeds
• Two unknowns!
Elastic Collisions in One
Dimension

6. • Do some algebra (page 176, if you are interested)
• vA – vB = vA’ – vB’
Elastic Collisions

7. • 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
Example

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