1. MOMENTUM AND COLLISIONS

2. 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. MOMENTUM

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

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. 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. PROBLEM 3

12. The brakes exert a 640 N force on a car weighing 15689 N and moving at 20 m/s. The car finally stops. A) What is the car’s mass? B) What is the car’s initial momentum? C) 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? PROBLEM 6

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. Glider A of mass.355 kg moves along a frictionless air track with a velocity of.095 m/s. It collides with a glider B of mass.710kg moving in the same direction at a speed of.045m/s. After collision glider A continues in the same direction with a velocity of.035 m/s. What is the velocity of glider B after collision? PROBLEM 11

20. 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) INTERNAL FORCES

21. External force is a force exerted by an object outside the system. Example: if car A was our system, and it collides with car B. Then the force car B exerts on car A is an external force. EXTERNAL FORCES

22. 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? PROBLEM 17

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

26. COLLISIONS INELASTIC  Momentum is conserved  Some kinetic energy is changed into other forms ELASTIC  Momentum is conserved.  Energy is conserved.

27. ELASTIC COLLISIONS 1 2 3

28. INELASTIC COLLISIONS

29. A 15-kg medicine ball is thrown at a velocity of 20 km/hr to a 60-kg person who is at rest on ice. The person catches the ball and subsequently slides with the ball across the ice. Determine the velocity of the person and the ball after the collision. Such a motion can be considered as a collision between a person 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 person to gain momentum. After the collision, the ball and the person travel with the same velocity ("v") across the ice.

30. Before Collision After Collision Person0 60 * v Medicine ball 300 15 * v Total300300

31. Before Collision After Collision Granny 80 * 6 = 480 80 * v Ambrose0 40 * v Total480480

32. Before Collision After Collision Truck 3000 * 10 = 30 000 3000 * v Car0 1000 * 15 = 15 000 Total 30 000

41. Elastic

44. 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 a totally 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.)

45. KE and Collisions Elastic KE is conserved: no sound or heat produced sub atomic particles, repelling magnets, a “perfect” super ball Inelastic (partially elastic) some KE is lost as heat or sound Is a broad range containing most collisions Completely Inelastic more KE is lost as heat or sound the colliding objects stick together

46. PROBLEM 20 A 2575 kg van runs into the back of a 825kg 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.

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