The **Law of Conservation of Momentum **states that the sum total of the momentum of a system of bodies before interaction equals the sum total of the momentum of the system of bodies after interaction.

The **Law of Conservation of Energy** states that the sum total of the energy possessed by a system remains constant, although it may be converted from one form into another.

An **elastic collision** is one in which the total kinetic energy of a system of bodies before collision equals the total kinetic energy of the system of bodies after collision. The total kinetic energy of a system of bodies experiencing elastic collision is conserved.

An **inelastic collision** is one in which the total kinetic energy of a system of bodies before collision does not equal the total kinetic energy of the system of bodies after collision. The total kinetic energy of a system of bodies experiencing inelastic collision is not conserved.

KEmechanical = m**v**exp2/2 PEgravitational = m**g**h PEelastic = kxexp2/2

KEbefore = KEafter KEbefore - KEafter = 0(for elastic collisions)

1. A 10,000-kg railroad car traveling at a speed of 24.0 m/s strikes an identical car at rest. If the cars lock together as a result of the collision, what is their common speed afterward?

2. Calculate the recoil velocity of a 5.0-kg rifle that shoots a 0.050-kg bullet at a speed of 120 m/s.

3. A billiard ball of mass m moving with a speed v collides head-on with a second ball of equal mass at rest (v2 = 0). Calculate are the speeds of the two balls after the collision, assuming it to be elastic.

4. A billiard ball of mass 1.0 kg and traveling with a velocity of 1.7 m/s due East collides head-on (linearly) with a ball of identical mass traveling at 3.4 m/s due West. Calculate the respective velocities of the balls after collision, assuming it to be elastic.

5. A proton of mass 1.01 u (unified atomic mass unit) traveling with a speed of 3.60 x 10exp4 m/s has an elastic head-on collision with a helium nucleus

(mHe nucleus = 4.00 u) initially at rest. What are the velocities of the proton and helium nucleus after the collision? (Note: 1.00 u = 1.66 x 10exp-27 kg)

6. Based on your solution of problem 1 above, calculate the how much of the initial kinetic energy is transformed into thermal or other forms of energy.

7. A billiard ball moving with speed v1 = 3.0 m/s in the +x direction strikes an equal mass ball initially at rest. The two balls are observed to move off at 45 degrees with respect to the +x axis, ball 1 above the x axis and ball 2 below the x axis. Calculate the speeds of the two balls. (Think!)

Cycle II AP Physics

John Dewey High School

Mr. Klimetz