1. Momentum and Its Conservation
Chapter 9 Notes
Momentum and Its Conservation

2. Section 9.1 Objectives Define the momentum of an object.
Determine the impulse given to an object.
Calculate the momentum and impulse of an object.

3. Momentum
p = mv
Units: kg*m/s

4. Practice Problems
A 2250 kg pickup truck has a velocity of 25 m/s to the east. What is the momentum of the truck?
What velocity must a 1210 kg car have in order to have the same momentum as the pickup truck in the previous problem?

5. Impulse and Momentum
Recall Newton’s Second Law

6. Impulse
FΔt

7. Impulse-Momentum Theorem
FΔt = ρf – ρi
Momentum and impulse are both vectors, so signs are important!!

8. Practice Problem
A 2200 kg vehicle traveling at 26 m/s can be stopped in 21 s by gently applying the brakes. It can be stopped in 3.8 s if the driver slams on the brakes, or in 0.22 s if it hits a concrete wall. What average force is exerted on the vehicle in each of these stops?

9. Saving Lives with Impulse-Momentum Theorem
What happens to the driver when a crash suddenly stops a car?

10. Section 9.2 Objectives
Relate Newton’s third law to conservation of momentum in collisions. 
Identify conditions that momentum is conserved. 
Solve conservation of momentum problem.

11. Law of Conservation of Momentum
pi = pf
pi,A + pi,B = pf,A + pf.B

12. Conditions for Conservation of Momentum
Closed system
Isolated system

13. Conservation of Momentum

15. Practice Problem
A 76 kg boater, initially at rest in a stationary 45 kg boat, steps out of the boat and onto the dock. If the boater moves out of the boat with a velocity of 2.5 m/s to the right, what is the final velocity of the boat?

16. Inelastic Collisions
Example: meteorite collides head on with Earth, becoming buried in Earth
mAvi + mBvi = (mA + mB)vf

17. Practice Problem
A 1850 kg luxury sedan stopped at a traffic light is struck from the rear by a compact car with a mass of 975 kg. The two cars become entangled as a result of the collision. If the compact car was moving at a velocity of 22.0 m/s to the north before the collision, what is the velocity of the entangled mass after the collision?

18. Elastic Collisions

19. Practice Problem
A kg marble moving to the right at m/s makes an elastic head on collision with a kg shooter marble moving to the left at m/s. After the collision, the smaller marble moves to the left at m/s. Assume that neither marble rotates before or after the collision and that both marbles are moving on a frictionless surface. What is the velocity of the kg marble after the collision?