Chapter 8 QuickCheck Questions

QuickCheck 8.2 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 1/4. 1/2. No change since the radius doesn’t change. 2. 4. STT1.2 Slide 8-38 2

QuickCheck 8.2 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 1/4. 1/2. No change since the radius doesn’t change. 2. 4. STT1.2 Slide 8-39 3

QuickCheck 8.3 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 new force: the centripetal force. A new force: the centrifugal force. One or more of our familiar forces pushing outward. One or more of our familiar forces pulling inward. I have no clue. Answer: D Slide 8-44 4

QuickCheck 8.3 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 new force: the centripetal force. A new force: the centrifugal force. One or more of our familiar forces pushing outward. One or more of our familiar forces pulling inward. I have no clue. Answer: D The rules about what is or is not a force haven’t changed. Force must be exerted at a point of contact (except for gravity). Force must have an identifiable agent doing the pushing or pulling. The net force must point in the direction of acceleration (Newton’s second law). Slide 8-45 5

QuickCheck 8.4 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? Gravity Air resistance Friction Normal force Tension in the string Answer: D Slide 8-46 6

QuickCheck 8.4 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? Gravity Air resistance Friction Normal force Tension in the string Answer: D Slide 8-47 7

QuickCheck 8.6 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? Answer: D Slide 8-66 8

QuickCheck 8.6 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? Answer: D Slide 8-67 9

QuickCheck 8.7 A coin sits on a turntable as the table steadily rotates ccw. What force or forces act in the plane of the turntable? Answer: D Slide 8-68 10

QuickCheck 8.7 A coin sits on a turntable as the table steadily rotates ccw. What force or forces act in the plane of the turntable? Answer: D Slide 8-69 11

QuickCheck 8.8 Two coins are on a turntable that steadily speeds up, starting from rest, with a ccw rotation. Which coin flies off the turntable first? Coin 1 flies off first. Coin 2 flies off first. Both coins fly off at the same time. We can’t say without knowing their masses. Answer: D Slide 8-70 12

QuickCheck 8.8 Two coins are on a turntable that steadily speeds up, starting from rest, with a ccw rotation. Which coin flies off the turntable first? Coin 1 flies off first. Coin 2 flies off first. Both coins fly off at the same time. We can’t say without knowing their masses. Answer: D Slide 8-71 13

QuickCheck 8.11 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. STT1.2 Slide 8-82 14

QuickCheck 8.11 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. STT1.2 The track is above the car, so the normal force of the track pushes down. Slide 8-83 15

QuickCheck 8.11 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? STT1.2 The track is above the car, so the normal force of the track pushes down. Slide 8-83 16

QuickCheck 8.11 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? Fc = F track + Fg (note all are toward the center, positive) mV2 / r = 0 + mg V2= rg (30) 2 = r (10) r = 90 m STT1.2 The track is above the car, so the normal force of the track pushes down. Slide 8-83 17

A 1 kg plane moves in a circle (radius of 0. 5 m) at 2 m/s A 1 kg plane moves in a circle (radius of 0.5 m) at 2 m/s . Find the angle ϴ made between the cord and the vertical.

A 1 kg plane moves in a circle (radius of 0. 5 m) at 2 m/s A 1 kg plane moves in a circle (radius of 0.5 m) at 2 m/s . Find the angle ϴ 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 (ϴ) = 8 / 10 So, ϴ = 38.7 o

QuickCheck 13.1 The force of Planet Y on Planet X is ___ the magnitude of . X on Y One quarter. One half. The same as. Twice. Four times. Slide 13-29 20

QuickCheck 13.1 The force of Planet Y on Planet X is ___ the magnitude of . X on Y One quarter. One half. The same as. Twice. Four times. Slide 13-30 21

QuickCheck 13.2 The gravitational force between two asteroids is 1,000,000 N. What will the force be if the distance between the asteroids is doubled? 250,000 N. 500,000 N. 1,000,000 N. 2,000,000 N. 4,000,000 N. Slide 13-31 22

QuickCheck 13.2 The gravitational force between two asteroids is 1,000,000 N. What will the force be if the distance between the asteroids is doubled? 250,000 N. 500,000 N. 1,000,000 N. 2,000,000 N. 4,000,000 N. Slide 13-32 23

QuickCheck 13.4 Planet X has free-fall acceleration 8 m/s2 at the surface. Planet Y has twice the mass and twice the radius of planet X. On Planet Y g = 2 m/s2. g = 4 m/s2. g = 8 m/s2. g = 16 m/s2. g = 32 m/s2. Slide 13-37 24

QuickCheck 13.4 Planet X has free-fall acceleration 8 m/s2 at the surface. Planet Y has twice the mass and twice the radius of planet X. On Planet Y g = 2 m/s2. g = 4 m/s2. g = 8 m/s2. g = 16 m/s2. g = 32 m/s2. Slide 13-38 25

QuickCheck 13.6 Which system has a greater gravitational force of attraction? System A. System B. They have the same gravitational force. Slide 13-46 26

QuickCheck 13.6 Which system has a greater gravitational force? System A. System B. They have the same gravitational force. Slide 13-47 27

QuickCheck 13.7 Two satellites have circular orbits with the same radius. Which has a higher speed? The one with more mass. The one with less mass. They have the same speed. Slide 13-58 28

QuickCheck 13.7 Two satellites have circular orbits with the same radius. Which has a higher speed? The one with more mass. The one with less mass. They have the same speed. Slide 13-59 29

QuickCheck 13.8 Two identical satellites have different circular orbits. Which has a higher speed? The one in the larger orbit. The one in the smaller orbit. They have the same speed. Slide 13-60 30

QuickCheck 13.8 Two identical satellites have different circular orbits. Which has a higher speed? The one in the larger orbit. The one in the smaller orbit. They have the same speed. Slide 13-61 31

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.

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 / r2 = mV2 / r M = V2 r / G M = (70)2 (100) / G M = 490,000 / G

QuickCheck 12.1 Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A. The angular velocity of A is twice that of B. The angular velocity of A equals that of B. The angular velocity of A is half that of B. Answer: B Slide 12-28 34

QuickCheck 12.1 Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A. The angular velocity of A is twice that of B. The angular velocity of A equals that of B. The angular velocity of A is half that of B. Answer: B Slide 12-29 35

QuickCheck 12.1 Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A. The LINEAR velocity of A is twice that of B. The LINEAR velocity of A equals that of B. The LINEAR velocity of A is half that of B. Answer: B Slide 12-28 36

QuickCheck 12.1 Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A. The LINEAR velocity of A is twice that of B. The LINEAR velocity of A equals that of B. The LINEAR velocity of A is half that of B. Answer: B Slide 12-29 37

Where should a student place the fulcrum to balance this massless 1 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 .

Where should a student place the fulcrum to balance this massless 1 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) ---------------------------- (0.8 + 1.2) = 1.84 / 2 = 0.92 m