1. CHAPTER 7 MOMENTUM AND COLLISIONS

2. MOMENTUM
Momentum is the product of the mass and velocity of a body. Momentum is a vector quantity that has the same direction as the velocity of the object.

3. MOMENTUM

4. PROBLEM 1
A 2250 kg pickup truck has a velocity of 25 m/s to the east. What is the momentum of the truck?

5. IMPULSE-MOMENTUM THEOREM
Impulse is the product of the average force and the time interval during which the force is exerted.

7. Applications of Impulse Momentum Theorem
Used to determine stopping distances and safe following distances of cars and trucks.
Used in designing safety equipment that reduces force exerted on the object during collisions. Example-nets and giant air mattresses for fire-fighters.
Also used in sports equipment and games.

9. PROBLEM 3 A baseball of mass 0.14 kg is moving at 35 m/s.
A) Find the momentum of the baseball.
B) Find the velocity of a bowling ball, mass 7.26 kg, if its momentum is the same as the baseball.

12. PROBLEM 6
The brakes exert a 640 N force on a car weighing N and moving at 20 m/s. The car finally stops.
What is the car’s mass?
What is the car’s initial momentum?
What is the change in the car’s momentum?
D) How long does the braking force act on the car to bring it to a halt?

16. CONSERVATION OF MOMENTUM
States that the momentum of any closed, isolated system does not change.
Isolated System has no net force acting on it.
Closed System is a system in which objects neither enter nor leave .

17. PROBLEM 11
Glider A of mass kg moves along a frictionless air track with a velocity of m/s. It collides with a glider B of mass kg moving in the same direction at a speed of m/s. After collision glider A continues in the same direction with a velocity of m/s. What is the velocity of glider B after collision?

20. INTERNAL FORCES
Internal forces are forces between objects within a system.
Example: If we consider a single car as our system, forces are exerted on objects within the car during a collision (i.e. a crash dummy)

21. INTERNAL FORCES

22. EXTERNAL FORCES
External force is a force exerted by an object outside the system.
Example: Our single car from the previous example is still considered our system. If the car collides with a tree, then the force the tree exerts on the car is an external force.

23. EXTERNAL FORCES

24. PROBLEM 17
Two campers dock a canoe. One camper steps on the dock. This camper has a mass of 80 kg and moves forward at 4 m/s. With what speed and direction do the canoe and the other camper move if their combined mass is 110 kg?

27. Types of Collisions
ELASTIC – objects are apart after the collision
INELASTIC – objects “stick” together after the collision

28. COLLISIONS INELASTIC Momentum is conserved
Some KE is changed into other forms
TOTALLY ELASTIC
Momentum is conserved.
KE is conserved.

29. ELASTIC COLLISIONS

30. INELASTIC COLLISIONS

31. SKATER/MEDICINE BALL EXAMPLE
A 15 kg medicine ball is thrown at a velocity of 20 km/hr to a 60 kg skater who is at rest on ice. The skater catches the ball and slides with the ball across the ice. Determine the velocity of the skater and the ball after the collision.

32. The collision occurs between a skater and a medicine ball
The collision occurs between a skater and a medicine ball. Before the collision, the ball has momentum and the person does not. The collision causes the ball to lose momentum and the skater to gain momentum. After the collision, the ball and the skater travel with the same velocity ("v") across the ice.

33. SKATER/MEDICINE BALL EX
Before Collision
After Collision
Skater
60 * v
Medicine ball
300
15 * v
Total

34. GRANNY/RALPH EXAMPLE

35. GRANNY/RALPH EXAMPLE Before Collision After Collision Granny
80 * 6 = 480
80 * v
Ralph
40 * v
Total
480

36. CAR/TRUCK EXAMPLE

37. CAR/TRUCK EXAMPLE Before Collision After Collision Truck
3000 * 10 =
3000 * v
Car
1000 * 15 =
Total
30 000

46. Elastic

47. Elastic

48. Elastic

49. Above is a representation of  3 bullets with equal mass running into 3 blocks of wood with equal mass. The first bullet passes through the block and maintains much of its original momentum   As a result, very little momentum gets transferred to the block. The second bullet, expands as it enters the block of wood which prevents it from passing all the way through it.  As a result, most of its momentum gets transferred to the block.  (This is an inelastic collision.) The third bullet (a rubber bullet) bounces off the block transferring all of it's own momentum and then borrowing some more from the block.  This has the most momentum transferred to the block.  (This is an elastic collision.)

50. KE and Collisions Totally (Perfectly) Elastic Collision
KE is conserved: no sound or heat produced
Example: sub atomic particles (electrons), attracting fields
(Partially) Elastic Collision
some KE is lost as heat or sound
Is a broad range containing most collisions
Example: billiard balls

51. KE and Collisions Completely Inelastic Collision
KE is conserved: no sound or heat produced
Example: sub atomic particles (electrons), repelling fields
Inelastic Collision
more KE is lost as heat or sound the colliding objects stick together
Example: Coupling railroad cars

52. PROBLEM 20
A 2575 kg van runs into the back of a 825 kg compact car at rest. They move off together at 8.5 m/s. Assuming no friction with the ground, find the initial speed of the van.

54. PROBLEM 21
A 5g bullet is fired with a velocity of 100 m/s toward a 10 kg stationary solid block resting on a frictionless surface. What is the change in momentum of the bullet if it becomes embedded in the block?