Momentum Review. Momentum Expressed in (SI unit): kg m/s Commonly used symbols: p Conserved: yes Expressed in other quantities: p = mv

Transcription

1 Momentum Review Momentum Expressed in (SI unit): kg m/s Commonly used symbols: p Conserved: yes Expressed in other quantities: p = mv

2 Chapter 7

3 What is momentum? The momentum of an object is defined as the object's 1. mass times it acceleration. 2. mass times its velocity. 3. force times its acceleration. 4. force times the time interval.

4 What is momentum? The momentum of an object is defined as the object's mass times its velocity (p=m x v)

5 Which has more momentum? Which has more momentum, a large truck moving at 30 miles per hour or a small truck moving at 30 miles per hour? 1. The large truck 2. The small truck 3. Both have the same momentum.

6 Which has more momentum? Which has more momentum, a large truck moving at 30 miles per hour or a small truck moving at 30 miles per hour? The large truck

7 Compare the two Compared to a sports car moving at 30 miles per hour, the same sports car moving at 60 miles per hour has 1. the same momentum. 2. twice as much momentum. 3. four times as much momentum.

8 Compare the two Compared to a sports car moving at 30 miles per hour, the same sports car moving at 60 miles per hour has twice as much momentum

9 Momentum =? The momentum change of an object is equal to the 1. force acting on it. 2. velocity change of the object. 3. impulse acting on it. 4. object's mass times the force acting on it.

10 Momentum =? The momentum change of an object is equal to the impulse acting on it

11 Increase golf ball momentum? In order to increase the final momentum of a golf ball, we could 1. increase the force acting on it. 2. increase the time of contact with the ball. 3. follow through when hitting the ball. 4. swing as hard as possible. 5. all of the above

12 Increase golf ball momentum? In order to increase the final momentum of a golf ball, we could 1. increase the force acting on it. 2. increase the time of contact with the ball. 3. follow through when hitting the ball. 4. swing as hard as possible. 5. all!!!!

13 Why? The reason padded dashboards are used in cars is that they * increase the force of impact in a collision *. increase the time of impact in a collision. *. decrease the momentum of a collision. *. decrease the impulse in a collision.

14 Why? The reason padded dashboards are used in cars is that they * increase the time of impact in a collision

15 Conservation of momentum Momentum of a system is conserved only when 1. there are no forces acting on the system. 2. there is no net external force acting on the system. 3. there are no internal forces acting on the syste 4. the system is not moving. 5. the system has zero momentum

16 Conservation of momentum Momentum of a system is conserved only when * there is no net external force acting on the system

17 Elastic collision. A collision is considered elastic if. *there is no sound generated during the collision. * there is no lasting deformation. * the objects that collide don't get hot. * after the collision, the objects have the same shape as before the collision. * all of the above.

18 Elastic collision. A collision is considered elastic if *there is no sound generated during the collision. * there is no lasting deformation. * the objects that collide don't get hot. * after the collision, the objects have the same shape as before the collision. * all!!!!!

19 How does she do it? Suppose a girl is standing on a pond where there is no friction between her feet and the ice. In order to get off the ice, she can *bend over touching the ice in front of her, then bring her feet to her hands. * throw something in the direction opposite to that in which she wants to go. * walk very slowly on tiptoe. * get on her hands and knees and crawl off the ice.

20 How does she do it? Suppose a girl is standing on a pond where there is no friction between her feet and the ice. In order to get off the ice, she can * throw something in the direction opposite to that in which she wants to go

21 The train is coming A freight train rolls along a track with considerable momentum. If it were to roll at the same speed but had twice as much mass, its momentum would be * zero. * doubled. * quadrupled. *unchanged.

22 The train is coming A freight train rolls along a track with considerable momentum. If it were to roll at the same speed but had twice as much mass, its momentum would be doubled

23 See them fall Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has a higher * speed. *acceleration. * momentum.

24 See them fall Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has a higher * momentum

25 Watch the ball. In order to catch a ball, a baseball player moves his or her hand backward in the direction of the ball's motion. Doing this reduces the force of impact on the player's hand principally because * the velocity of the hand is reduced. * the momentum of impact is reduced. * the time of impact is increased. * the time of impact is decreased.

26 Watch the ball. In order to catch a ball, a baseball player moves his or her hand backward in the direction of the ball's motion. Doing this reduces the force of impact on the player's hand principally because * the time of impact is increased.

27 How about that cannon? A cannon fires a cannonball. The speed of the cannonball will be the same as the speed of the recoiling cannon * because momentum is conserved. * because velocity is conserved. *because both velocity and momentum are conserved * if the mass of the cannonball equals the mass of the cannon.

28 How about that cannon? A cannon fires a cannonball. The speed of the cannonball will be the same as the speed of the recoiling cannon * if the mass of the cannonball equals the mass of the cannon.

29 Apples falling from a tree The force of an apple hitting the ground depends upon A. air resistance on the apple as it falls. B. the speed of the apple just before it hits. C. the time of impact with the ground. D. whether or not the apple bounces. E. all of the above

30 Apples falling from a tree The force of an apple hitting the ground depends upon A. air resistance on the apple as it falls. B. the speed of the apple just before it hits. C. the time of impact with the ground. D. whether or not the apple bounces. E. all of the above

31 Bend your knees! When you jump off a step, you usually bend your knees as you reach the ground. By doing this, the time of the impact is about 10 times more what it would be in a stiff-legged landing and the average force on your body is reduced by 1. less than 10 times. 2. more than 10 times. 3. about 10 times

32 Bend your knees! When you jump off a step, you usually bend your knees as you reach the ground. By doing this, the time of the impact is about 10 times more what it would be in a stiff-legged landing and the average force on your body is reduced by about 10 times

33 Connect the train A moving freight car runs into an identical car at rest on the track. The cars couple together. Compared to the velocity of the first car before the collision, the velocity of the combined cars after the collision is twice as large. the same. one half as large. zero.

34 Connect the train A moving freight car runs into an identical car at rest on the track. The cars couple together. Compared to the velocity of the first car before the collision, the velocity of the combined cars after the collision is one half as large.

35 A sticky situation A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball, both are set in motion with a combined momentum that is less than 1 unit. more than 1 unit. 1 unit

36 A sticky situation A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball, both are set in motion with a combined momentum that is 1 unit

37 Play catch? Suppose an astronaut in outer space wishes to play a solitary "throw, bounce, and catch" game by tossing a ball against a very massive and perfectly elastic concrete wall. If the ball is as massive as the astronaut, then the astronaut will catch one bounce only. the astronaut will never catch the first bounce. the astronaut's time between catches will decrease as the game progresses

38 Play catch? Suppose an astronaut in outer space wishes to play a solitary "throw, bounce, and catch" game by tossing a ball against a very massive and perfectly elastic concrete wall. If the ball is as massive as the astronaut, then the astronaut will never catch the first bounce.

39 Watch out! A golf ball moving forward with 1 unit of momentum strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with a momentum of less than 1 unit. more than 1 unit. 1 unit.

40 Watch out! A golf ball moving forward with 1 unit of momentum strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with a momentum of more than 1 unit.

41 Want to rollerblade? While rollerblading, Granny collides with her tiny grandson John who is at rest. Ignoring any friction effects, John's speed after the collision will be greatest when he and Granny make a bouncing collision, each going separate ways. Granny catches him and they both move together

42 Want to rollerblade? While rollerblading, Granny collides with her tiny grandson John who is at rest. Ignoring any friction effects, John's speed after the collision will be greatest when he and Granny make a bouncing collision, each going separate ways.

43 Help me push A small economy car (low mass) and a limousine (high mass) are pushed from rest across a parking lot, equal distances with equal forces. The car that receives the greater impulse is the small economy car. limousine. neither A nor B (same for each)

44 Help me push A small economy car (low mass) and a limousine (high mass) are pushed from rest across a parking lot, equal distances with equal forces. The car that receives the greater impulse is the limousine.

45 . A 4-kg ball has a momentum of 12 kg m/s. What is the ball's speed? 3 m/s 4 m/s 12 m/s 48 m/s

46 . A 4-kg ball has a momentum of 12 kg m/s. What is the ball's speed? 3 m/s

47 How big is the ball? A ball is moving at 4 m/s and has a momentum of 48 kg m/s. What is the ball's mass? 4 kg 12 kg 48 kg 192 kg

48 How big is the ball? A ball is moving at 4 m/s and has a momentum of 48 kg m/s. What is the ball's mass? 12 kg

49 How much momentum? A 1-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-kg bowling ball that is initially at rest. The bowling ball with its putty passenger will then be set in motion with a momentum of 0 kg m/s. 1 kg m/s. 2 kg m/s. 5 kg m/s. more than 5 kg m/s.

50 How much momentum? A 1-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-kg bowling ball that is initially at rest. The bowling ball with its putty passenger will then be set in motion with a momentum of 1 kg m/s.

51 Watch out! A 10-kg cement block moving horizontally at 2.0 m/s plows into a pillow and comes to a stop in 0.5 s. What is the average impact force on the pillow? {hint: Impulse =change in momentum}

52 Watch out! A 10-kg cement block moving horizontally at 2.0 m/s plows into a pillow and comes to a stop in 0.5 s. What is the average impact force on the pillow? Mass=, Speed=, Time= ; Force x Time=change in (mass x velocity) {hint: Impulse =change in momentum}

53 Watch out! A 10-kg cement block moving horizontally at 2.0 m/s plows into a pillow and comes to a stop in 0.5 s. What is the average impact force on the pillow? Mass= 10kg, Speed=2.0 m/s, Time=0.5s; F x 0.5s = 10kg x 2.0m/s = F x 0.5 s = N Force x Time=change in (mass x velocity) {hint: Impulse =change in momentum}

54 Wow, together again A 8.0-kg blob of clay moving horizontally at 2.0 m/s hits a 4.0-kg blob of clay at rest. What is the speed of the two blobs stuck together immediately after the collision? {hint: p1 + p2 before = mass1 + mass 2 (v)}

55 Wow, together again A 8.0-kg blob of clay moving horizontally at 2.0 m/s hits a 4.0-kg blob of clay at rest. What is the speed of the two blobs stuck together immediately after the collision? {hint: p1 + p2 before = mass1 + mass 2 (v)}

56 Wow, together again A 8.0-kg blob of clay moving horizontally at 2.0 m/s hits a 4.0-kg blob of clay at rest. What is the speed of the two blobs stuck together immediately after the collision? 8kg x 2.0 m/s + 4 x 0 = 8kg + 4kg (v) {hint: p1 + p2 before = mass1 + mass 2 (v)}

57 Get out of the way! An 80-kg cart moving at 70 km/h collides head-on with an approaching 120-kg cart moving at 40 km/h (in the opposite direction). If the two carts stick together, what will be their speed?

58 Get out of the way! An 80-kg cart moving at 70 km/h collides head-on with an approaching 120-kg cart moving at 40 km/h (in the opposite direction). If the two carts stick together, what will be their speed? {hint: p1 - p2 before = mass1 + mass 2 (v)}

59 Change in momentum A 10-kg bowling ball moving at 4.0 m/s bounces off a spring at about the same speed that it had before bouncing. What is the change in momentum of the bowling ball? {hint: mass x velocity x 2}