2. Unit 7.2 Conservation of Momentum Teacher: Dr. Van Der Sluys

3. Objectives Collisions Law of Conservation of Momentum Simple Collision Problems –Elastic –Inelastic

4. Momentum For an individual object p = mV For a system involving multiple objects  p =  m n v n Where m n v n are the momentums of each of the individual objects in the system.

5. Collisions Elastic collisions between objects result in rebounds, so that the total kinetic energy of the system remains the same. Inelastic collisions result when the objects in the system stick together and there is a conversion of some kinetic energy into other forms of energy.

6. Law of Conservation of Momentum For any two body system the total momentum before and after a collision must be equal. m 1 v 1 + m 2 v 2 = m 1 v 1 ’ + m 2 v 2 ’ The law of Conservation of momentum states that the total momentum of an isolated system is always constant.

7. Conservation of Momentum - Rifle recoil What is the recoil velocity of a 6.0 kg shot gun that shoots a 0.150 kg deer slug at a speed of 120 m/s? Hint: Draw a vector diagram representing both the velocity and momentum of both the bullet and the gun before and after the bullet is fired.

8. Conservation of Momentum - Simple Inelastic Example An empty 10,000 kg railroad car traveling at a speed of 24.0 m/s strikes an identical railroad car that is stationary. If the couplings cause the cars to lock together as a result of the collision, what is their velocity after the collision?

9. Conservation of Momentum - Simple Inelastic Example An empty 10,000 kg railroad car traveling at a speed of 24.0 m/s strikes loaded railroad car having a mass of 20,000 kg that is stationary. If the couplings cause the cars to lock together as a result of the collision, what is their velocity after the collision?

10. Conservation of Momentum - Simple Inelastic Example An empty 10,000 kg railroad car traveling at a speed of 24.0 m/s strikes loaded railroad car having a mass of 20,000 kg that is moving with a velocity of -12.0 m/s. If the couplings cause the cars to lock together as a result of the collision, what is their velocity after the collision?

11. Simple Systems Involving Elastic Collisions http://www.hazelwood.k12.mo.us/~grichert/ex plore/dswmedia/airtrack.htmhttp://www.hazelwood.k12.mo.us/~grichert/ex plore/dswmedia/airtrack.htm Try some of the following and predict what will happen after the elastic collision. –m 1 = m 2, v 1 = 5.0 m/s and v 2 = 0 m/s (Can you predict? How do you know?) –m 1 = 1.0 kg and m 2 = 2.0 kg, v 1 = 5.0 m/s and v 2 = 0 m/s –m 1 = m 2, v 1 = 5.0 m/s and v 2 = -5.0 m/s –Try others of your choice (Can you predict? If not, why not?)

12. A Really Complicated System Involving Elastic Collisions in Two Dimensions http://en.wikipedia.org/wiki/Elastic_collision