Think about Action Reaction Pairs. What is the action and what is the reaction? This is first a problem of ordinary pennies (Common sense).

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1 Quest Chapter 06 1 When you drop a rubber ball on the floor it bounces almost to its original height. What causes the ball to bounce? 1. The ball attempts to return to its original position. 2. The floor pushes up on the ball harder then the ball pushes down on the floor. 3. Air forced out upon contact causes a temporary vacuum which sucks the ball up. 4. The force of the floor on the ball causes it to bounce upward. 2 Ken and Joanne are astronauts floating some distance apart in space. They are joined by a safety cord whose ends are tied around their waists. If Ken starts pulling on the cord, what will happen? 1. The move toward each other. 2. Joanne will move toward Ken while Ken remains stationary. 3. Ken will move toward Joanne while Joanne remains stationary. 4. Neither will move. Think about Action Reaction Pairs. What is the action and what is the reaction? This is first a problem of ordinary pennies (Common sense). If you must, think of the Action Reaction Pairs in the problem. The action acts on whom? 3 (part 1 of 2) A fast-moving VW Beetle traveling at 54 mph hits a mosquito hovering at rest above the road. Which bug experienced the largest force? 1. the VW 2. the insect 3. They experienced the same magnitude of force. 4. Unable to determine 4 (part 2 of 2) Which bug experienced the greatest acceleration? 1. Unable to determine. 2. the insect 3. the VW 4. Their acceleration is same. The reaction acts on whom? Think about Action Reaction Pairs. Use the second law of motion.

2 5 When you kick a soccer ball, you apply a force F1 to the ball. What force F2 does the soccer ball exert on your foot? 1. F1 = F2, acting in the same direction 2. F1 = F2, acting in opposite directions 3. F1 < F2 4. F2 < F1 5. There is no force F2. 6 Consider a tug-of-war contest between two people. Assume the rope is light and does not slip in either person s hands. What relationship would the two forces have? Who will win the contest? 1. The forces are not equal; luck, not force, determines the winner. 2. The forces are not equal; the person who pulls harder usually wins. 3. The forces are equal; usually the person who weighs more and has better footing wins. 4. The forces are equal; neither person can win. 7 If a book is sitting on a table, the force of gravity pulls it down. Why doesn t it fall? 1. The book is not heavy enough. 2. Gravity isn t pulling hard enough. 3. The table is pushing up on it with a force equal to the weight of the book. 8 The Earth exerts an 710 N gravitational force on a man. What force does the man exert on the Earth? Review the third law. Consider the rope. Is the tension in the rope the same everywhere? If so, consider the forces that cause the tension. Do the forces have the same magnitude? How would someone win? Think about Action Reaction Pairs.

3 9 Two students sit in identical office chairs facing each other. Bob has a mass of 95 kg, while Jim has a mass of 77 kg. Bob places his bare feet on Jim s knees, as shown to the right. Bob then suddenly pushes outward with his feet, causing both chairs to move. (see diagram) In this situation, while Bob s feet are in contact with Jim s knees, 1. None of these answers is correct. 2. Bob exerts a force on Jim, but Jim doesn t exert a force on Bob. 3. Each student exerts a force on the other, but Bob exerts a larger force. 4. Each student exerts a force on the other, but Jim exerts a larger force. 5. Neither student exerts a force on the other. 6. Each student exerts the same amount of force on the other. 10 As you stand on a floor, the floor exerts an upward force on you. Why are you not moved upward by this force? 1. The upward force is negligible. 2. The upward force is equal to your weight and the two forces cancel each other. 3. The upward force is less than your weight, so you do not move up. 4. The upward force is greater than your weight, but air pressure pushes you down. Without the air, you would be lifted up. 5. None of these 11 Identify the action-reaction pairs when a baseball is in flight. 1. All are wrong. 2. Action: Ball pulls down on Earth. Reaction: Earth pulls up on ball. Action: Air pushes ball. Reaction: Ball pushes air. 3. Action: Bat pushes ball forward. Reaction: Ball pulls up on Earth. Action: Ball pushes air. Reaction: Air pushes ball. 4. Action: Earth pulls down on ball. Reaction: Ball pulls up on Earth. Action: Air pushes ball. Reaction: Ball pushes air. 5. Action: Bat pushes ball backward. Reaction: Earth pulls down on ball. Action: Ball pushes air. Reaction: Air pushes ball. Note the Action Reaction Pairs. What can you say about the forces each student exerted on the other? Are you in equilibrium? What does in flight mean? Make sure to include all of the forces. Identify the Action Reaction Pairs.

4 12 Identify the action-reaction pairs when a baseball is being hit. 1. Action: bat hits ball. Reaction: ball hits the player. 2. None of these 3. Action: bat hits ball. Reaction: ball hits bat. 4. Action: ball hits bat. Reaction: bat hits the player. 5. Action: ball hits bat. Reaction: bat pushes the arm of the player. 13 When the athlete holds the barbell on his hand, the reaction force is the weight of the barbell on his hand. How does this force vary for the case where the barbell is accelerated upward? Downward? 1. Upward: the reaction force is less than the weight of the barbell; downward: the reaction force is less than the weight of the barbell. 2. Upward: the reaction force is greater than the weight of the barbell; downward: the reaction force is greater than the weight of the barbell. 3. Upward: the reaction force is greater than the weight of the barbell; downward: the reaction force is less than the weight of the barbell. 4. Upward: the reaction force is less than the weight of the barbell; downward: the reaction force is greater than the weight of the barbell. 5. All are wrong. Being hit means bat is in contact with the ball. Make sure to include all of the forces. Identify the Action Reaction Pairs. Think about applying a force to something against gravity of with gravity. Remember the elevator problems from the last chapter. Draw the FBD and include all of the forces. Draw one diagram for the before, one for the push-up, and one for the push-down. Make sure to draw the arrows proportionally correct.

5 14 What statement is correct? 1. You can exert greater force on the pedals you will exert smaller force on the pedals of a 2. You can exert greater force on the pedals you can exert greater force on the pedals of a 3. You will exert smaller force on the pedals you will exert smaller force on the pedals of a 4. All are wrong. 5. You will exert smaller force on the pedals you can exert greater force on the pedals of a 15 If a Mack truck and Honda Civic have a headon collision, upon which vehicle is the impact force greater and which vehicle experiences the greater acceleration? 1. The forces are the same; the accelerations are same. 2. The force on the truck is greater; the accelerations are the same. 3. The forces are the same; the Civic experiences the greater acceleration. 4. The forces are the same; the truck experiences the greater acceleration. 5. All are wrong. 16 Consider a stone at rest on the ground. There are two interactions that involve the stone. One is between the stone and the Earth; Earth pulls down on the stone and the stone pulls up on the Earth. What is the other interaction? 1. between the stone and the ground 2. between the ground and the Earth 3. between the Earth and air 4. All are wrong. 5. between the ground and air Read carefully. Use the Third Law to determine the sizes of the forces. Use the Second Law to determine the accelerations. Think of the first interation given as the whole Earth. Where is the stone? What is happening at that exact spot? (Think balancing force )

6 17 Imagine a horse pulling a cart; the horse and the cart move at the same velocity. Whether the horse and the cart are moving at a constant velocity or not is not important. Now, according to the laws of motion, the horse and the cart exert forces on each other. Which force is bigger? 1. Two forces are equal 2. Force exerted by the horse on the cart 3. Force exerted by the cart on the horse 4. Insufficient information to determine 18 A projectile moves along a parabolic path near the Earth s surface. What is the reaction to the Earth s gravitational force? 1. The force exerted by the projectile on the Earth. 2. The mass of the projectile. 3. The force of air friction. 4. The weight of the projectile. 5. None of these 19 The earth exerts a force of 2300 N on an orbiting communications satellite that is 39 miles above the Earth. What is the magnitude of the force the satellite will exert on the earth? Bigger means magnitude. Use the Third Law. Draw the FBD if you need help. Remember that the FBD has two objects. Remember that actions and reactions act on different objects. Use the Third Law.