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FOR SCIENTISTS AND ENGINEERS physics a strategic approach THIRD EDITION randall d. knight © 2013 Pearson Education, Inc. Chapter 8 QuickCheck Questions

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© 2013 Pearson Education, Inc. A toy car moves around a circular track at constant speed. It suddenly doubles its speed — a change of a factor of 2. As a result, the centripetal acceleration changes by a factor of A. 1/4. B. 1/2. C. No change since the radius doesn’t change. D. 2. E. 4. QuickCheck 8.2 Slide 8-38

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© 2013 Pearson Education, Inc. A toy car moves around a circular track at constant speed. It suddenly doubles its speed—a change of a factor of 2. As a result, the centripetal acceleration changes by a factor of A. 1/4. B. 1/2. C. No change since the radius doesn’t change. D. 2. E. 4. QuickCheck 8.2 Slide 8-39

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© 2013 Pearson Education, Inc. An ice hockey puck is tied by a string to a stake in the ice. The puck is then swung in a circle. What force or forces does the puck feel? A.A new force: the centripetal force. B.A new force: the centrifugal force. C.One or more of our familiar forces pushing outward. D.One or more of our familiar forces pulling inward. E.I have no clue. QuickCheck 8.3 Slide 8-44

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© 2013 Pearson Education, Inc. An ice hockey puck is tied by a string to a stake in the ice. The puck is then swung in a circle. What force or forces does the puck feel? A.A new force: the centripetal force. B.A new force: the centrifugal force. C.One or more of our familiar forces pushing outward. D.One or more of our familiar forces pulling inward. E.I have no clue. QuickCheck 8.3 The rules about what is or is not a force haven’t changed. 1. Force must be exerted at a point of contact (except for gravity). 2. Force must have an identifiable agent doing the pushing or pulling. 3. The net force must point in the direction of acceleration (Newton’s second law). Slide 8-45

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© 2013 Pearson Education, Inc. An ice hockey puck is tied by a string to a stake in the ice. The puck is then swung in a circle. What force is producing the centripetal acceleration of the puck? A. Gravity B. Air resistance C. Friction D. Normal force E. Tension in the string QuickCheck 8.4 Slide 8-46

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© 2013 Pearson Education, Inc. An ice hockey puck is tied by a string to a stake in the ice. The puck is then swung in a circle. What force is producing the centripetal acceleration of the puck? A. Gravity B. Air resistance C. Friction D. Normal force E. Tension in the string QuickCheck 8.4 Slide 8-47

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© 2013 Pearson Education, Inc. A coin sits on a turntable as the table steadily rotates ccw. The free-body diagrams below show the coin from behind, moving away from you. Which is the correct diagram? QuickCheck 8.6 Slide 8-66

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© 2013 Pearson Education, Inc. A coin sits on a turntable as the table steadily rotates ccw. The free-body diagrams below show the coin from behind, moving away from you. Which is the correct diagram? QuickCheck 8.6 Slide 8-67

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© 2013 Pearson Education, Inc. A coin sits on a turntable as the table steadily rotates ccw. What force or forces act in the plane of the turntable? QuickCheck 8.7 Slide 8-68

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© 2013 Pearson Education, Inc. A coin sits on a turntable as the table steadily rotates ccw. What force or forces act in the plane of the turntable? QuickCheck 8.7 Slide 8-69

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© 2013 Pearson Education, Inc. Two coins are on a turntable that steadily speeds up, starting from rest, with a ccw rotation. Which coin flies off the turntable first? QuickCheck 8.8 A.Coin 1 flies off first. B.Coin 2 flies off first. C.Both coins fly off at the same time. D.We can’t say without knowing their masses. Slide 8-70

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© 2013 Pearson Education, Inc. Two coins are on a turntable that steadily speeds up, starting from rest, with a ccw rotation. Which coin flies off the turntable first? QuickCheck 8.8 A.Coin 1 flies off first. B.Coin 2 flies off first. C.Both coins fly off at the same time. D.We can’t say without knowing their masses. Slide 8-71

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© 2013 Pearson Education, Inc. A roller coaster car does a loop- the-loop. Which of the free-body diagrams shows the forces on the car at the top of the loop? Rolling friction can be neglected. QuickCheck 8.11 Slide 8-82

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© 2013 Pearson Education, Inc. A roller coaster car does a loop- the-loop. Which of the free-body diagrams shows the forces on the car at the top of the loop? Rolling friction can be neglected. QuickCheck 8.11 The track is above the car, so the normal force of the track pushes down. Slide 8-83

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© 2013 Pearson Education, Inc. A roller coaster car does a loop- the-loop. If the minimum speed to navigate this loop is 30 m/s, what is the radius of the track? QuickCheck 8.11 The track is above the car, so the normal force of the track pushes down. Slide 8-83

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© 2013 Pearson Education, Inc. A roller coaster car does a loop- the-loop. If the minimum speed to navigate this loop is 30 m/s, what is the radius of the track? QuickCheck 8.11 The track is above the car, so the normal force of the track pushes down. Slide 8-83 Fc = F track + Fg (note all are toward the center, positive) mV 2 / r = 0 + mg V 2 = rg (30) 2 = r (10) r = 90 m

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© 2013 Pearson Education, Inc. A 1 kg plane moves in a circle (radius of 0.5 m) at 2 m/s. Find the angle made between the cord and the vertical.

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© 2013 Pearson Education, Inc. A 1 kg plane moves in a circle (radius of 0.5 m) at 2 m/s. Find the angle made between the cord and the vertical. Fc = (1)(2)^2 / (0.5) = 8 N Fg = mg = (1)(10) = 10 N Now use trig: Tan () = 8 / 10 So, = 38.7 o

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© 2013 Pearson Education, Inc. The force of Planet Y on Planet X is ___ the magnitude of. QuickCheck 13.1 A. One quarter. B. One half. C. The same as. D. Twice. E. Four times. Slide X on Y

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© 2013 Pearson Education, Inc. The force of Planet Y on Planet X is ___ the magnitude of. QuickCheck 13.1 A. One quarter. B. One half. C. The same as. D. Twice. E. Four times. Slide X on Y

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© 2013 Pearson Education, Inc. The gravitational force between two asteroids is 1,000,000 N. What will the force be if the distance between the asteroids is doubled? QuickCheck 13.2 A. 250,000 N. B. 500,000 N. C. 1,000,000 N. D. 2,000,000 N. E. 4,000,000 N. Slide 13-31

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© 2013 Pearson Education, Inc. The gravitational force between two asteroids is 1,000,000 N. What will the force be if the distance between the asteroids is doubled? QuickCheck 13.2 A. 250,000 N. B. 500,000 N. C. 1,000,000 N. D. 2,000,000 N. E. 4,000,000 N. Slide 13-32

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© 2013 Pearson Education, Inc. Planet X has free-fall acceleration 8 m/s 2 at the surface. Planet Y has twice the mass and twice the radius of planet X. On Planet Y QuickCheck 13.4 A. g = 2 m/s 2. B. g = 4 m/s 2. C. g = 8 m/s 2. D. g = 16 m/s 2. E. g = 32 m/s 2. Slide 13-37

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© 2013 Pearson Education, Inc. Planet X has free-fall acceleration 8 m/s 2 at the surface. Planet Y has twice the mass and twice the radius of planet X. On Planet Y QuickCheck 13.4 A. g = 2 m/s 2. B. g = 4 m/s 2. C. g = 8 m/s 2. D. g = 16 m/s 2. E. g = 32 m/s 2. Slide 13-38

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© 2013 Pearson Education, Inc. Which system has a greater gravitational force of attraction? QuickCheck 13.6 A. System A. B. System B. C. They have the same gravitational force. Slide 13-46

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© 2013 Pearson Education, Inc. Which system has a greater gravitational force? QuickCheck 13.6 A. System A. B. System B. C. They have the same gravitational force. Slide 13-47

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© 2013 Pearson Education, Inc. Two satellites have circular orbits with the same radius. Which has a higher speed? QuickCheck 13.7 A. The one with more mass. B. The one with less mass. C. They have the same speed. Slide 13-58

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© 2013 Pearson Education, Inc. Two satellites have circular orbits with the same radius. Which has a higher speed? QuickCheck 13.7 A. The one with more mass. B. The one with less mass. C. They have the same speed. Slide 13-59

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© 2013 Pearson Education, Inc. Two identical satellites have different circular orbits. Which has a higher speed? A. The one in the larger orbit. B. The one in the smaller orbit. C. They have the same speed. Slide QuickCheck 13.8

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© 2013 Pearson Education, Inc. Two identical satellites have different circular orbits. Which has a higher speed? A. The one in the larger orbit. B. The one in the smaller orbit. C. They have the same speed. Slide QuickCheck 13.8

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© 2013 Pearson Education, Inc. A really tiny planet named Dinky is orbiting a really tiny star named Biggerthandinky at a radius of 100 m. If the velocity of the really tiny planet is 70 m/s, find the mass of the star in terms of Newton’s Universal Constant G. Like, 30 G, or 8 G, etc.

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© 2013 Pearson Education, Inc. A really tiny planet named Dinky is orbiting a really tiny star named Biggerthandinky at a radius of 100 m. If the velocity of the really tiny planet is 70 m/s, find the mass of the star in terms of Newton’s Universal Constant G. Like, 30 G, or 8 G, etc. F g = F c GMm / r 2 = mV 2 / r M = V 2 r / G M = (70) 2 (100) / G M = 490,000 / G

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© 2013 Pearson Education, Inc. Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A. QuickCheck 12.1 A.The angular velocity of A is twice that of B. B.The angular velocity of A equals that of B. C.The angular velocity of A is half that of B. Slide 12-28

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© 2013 Pearson Education, Inc. Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A. QuickCheck 12.1 A.The angular velocity of A is twice that of B. B.The angular velocity of A equals that of B. C.The angular velocity of A is half that of B. Slide 12-29

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© 2013 Pearson Education, Inc. Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A. QuickCheck 12.1 A.The LINEAR velocity of A is twice that of B. B.The LINEAR velocity of A equals that of B. C.The LINEAR velocity of A is half that of B. Slide 12-28

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© 2013 Pearson Education, Inc. Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A. QuickCheck 12.1 A.The LINEAR velocity of A is twice that of B. B.The LINEAR velocity of A equals that of B. C.The LINEAR velocity of A is half that of B. Slide 12-29

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© 2013 Pearson Education, Inc. Where should a student place the fulcrum to balance this massless 1.6 m beam? The soccer ball has a mass of 0.8 kg and is located at 0.2 m from the left. The basketball has a mass of 1.2 kg and is located 0.2 m from the right.

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© 2013 Pearson Education, Inc. Where should a student place the fulcrum to balance this massless 1.6 m beam? The soccer ball has a mass of 0.8 kg and is located at 0.2 m from the left. The basketball has a mass of 1.2 kg and is located 0.2 m from the right. (0.8)(0.2) + (1.2)(1.4) ( ) = 1.84 / 2 = 0.92 m

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