PHYSICS FOR SCIENTISTS AND ENGINEERS A STRATEGIC APPROACH

PHYSICS FOR SCIENTISTS AND ENGINEERS A STRATEGIC APPROACH 4/E Chapter 12 Quick. Check Questions RANDALL D. KNIGHT © 2017 Pearson Education, Inc.

Quick. Check 12. 1 Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A. 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. © 2017 Pearson Education, Inc. Slide 12 -2

Quick. Check 12. 1 Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A. 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. © 2017 Pearson Education, Inc. Slide 12 -3

Quick. Check 12. 2 The fan blade is speeding up. What are the signs of ω and α? A. ω is positive and α is positive. B. ω is positive and α is negative. C. ω is negative and α is positive. D. ω is negative and α is negative. © 2017 Pearson Education, Inc. Slide 12 -4

Quick. Check 12. 2 The fan blade is speeding up. What are the signs of ω and α? A. ω is positive and α is positive. B. ω is positive and α is negative. C. ω is negative and α is positive. D. ω is negative and α is negative. © 2017 Pearson Education, Inc. Slide 12 -5

Quick. Check 12. 3 A baseball bat is cut in half at its center of mass. Which end is heavier? A. The handle end (left end) B. The hitting end (right end) C. The two ends weigh the same. © 2017 Pearson Education, Inc. Slide 12 -6

Quick. Check 12. 3 A baseball bat is cut in half at its center of mass. Which end is heavier? A. The handle end (left end) B. The hitting end (right end) C. The two ends weigh the same. © 2017 Pearson Education, Inc. Slide 12 -7

Quick. Check 12. 4 Which dumbbell has the larger moment of inertia about the midpoint of the rod? The connecting rod is massless. A. Dumbbell A. B. Dumbbell B. C. Their moments of inertia are the same. © 2017 Pearson Education, Inc. Slide 12 -8

Quick. Check 12. 4 Which dumbbell has the larger moment of inertia about the midpoint of the rod? The connecting rod is massless. A. Dumbbell A. B. Dumbbell B. C. Their moments of inertia are the same. Distance from the axis is more important than mass. © 2017 Pearson Education, Inc. Slide 12 -9

Quick. Check 12. 5 The four forces shown have the same strength. Which force would be most effective in opening the door? A. B. C. D. E. Force F 1 Force F 2 Force F 3 Force F 4 Either F 1 or F 3 © 2017 Pearson Education, Inc. Slide 12 -10

Quick. Check 12. 5 The four forces shown have the same strength. Which force would be most effective in opening the door? A. B. C. D. E. Force F 1 Force F 2 Force F 3 Force F 4 Either F 1 or F 3 © 2017 Pearson Education, Inc. Your intuition likely led you to choose F 1. The reason is that F 1 exerts the largest torque about the hinge. Slide 12 -11

Quick. Check 12. 6 Which third force on the wheel, applied at point P, will make the net torque zero? © 2017 Pearson Education, Inc. Slide 12 -12

Quick. Check 12. 6 Which third force on the wheel, applied at point P, will make the net torque zero? © 2017 Pearson Education, Inc. Slide 12 -13

Quick. Check 12. 7 A student gives a quick push to a puck that can rotate in a horizontal circle on a frictionless table. After the push has ended, the puck’s angular speed A. Steadily increases. B. Increases for awhile, then holds steady. C. Holds steady. D. Decreases for awhile, then holds steady. E. Steadily decreases. © 2017 Pearson Education, Inc. Slide 12 -14

Quick. Check 12. 7 A student gives a quick push to a puck that can rotate in a horizontal circle on a frictionless table. After the push has ended, the puck’s angular speed A. Steadily increases. B. Increases for awhile, then holds steady. C. Holds steady. D. Decreases for awhile, then holds steady. E. Steadily decreases. A torque changes the angular velocity. With no torque, the angular velocity stays the same. This is Newton’s first law for rotation. © 2017 Pearson Education, Inc. Slide 12 -15

Quick. Check 12. 8 Which object is in static equilibrium? © 2017 Pearson Education, Inc. Slide 12 -16

Quick. Check 12. 8 Which object is in static equilibrium? © 2017 Pearson Education, Inc. Slide 12 -17

Quick. Check 12. 9 What does the scale read? 500 N B. 1000 N C. 2000 N D. 4000 N A. Answering this requires reasoning, not calculating. © 2017 Pearson Education, Inc. Slide 12 -18

Quick. Check 12. 9 What does the scale read? 500 N B. 1000 N C. 2000 N D. 4000 N A. © 2017 Pearson Education, Inc. Slide 12 -19

Quick. Check 12. 10 A wheel rolls without slipping. Which is the correct velocity vector for point P on the wheel? © 2017 Pearson Education, Inc. Slide 12 -20

Quick. Check 12. 10 A wheel rolls without slipping. Which is the correct velocity vector for point P on the wheel? © 2017 Pearson Education, Inc. Slide 12 -21

Quick. Check 12. 11 Two buckets spin around in a horizontal circle on frictionless bearings. Suddenly, it starts to rain. As a result, A. The buckets speed up because the potential energy of the rain is transformed into kinetic energy. B. The buckets continue to rotate at constant angular velocity because the rain is falling vertically while the buckets move in a horizontal plane. C. The buckets slow down because the angular momentum of the bucket + rain system is conserved. D. The buckets continue to rotate at constant angular velocity because the total mechanical energy of the bucket + rain system is conserved. E. None of the above. © 2017 Pearson Education, Inc. Slide 12 -22

Quick. Check 12. 11 Two buckets spin around in a horizontal circle on frictionless bearings. Suddenly, it starts to rain. As a result, A. The buckets speed up because the potential energy of the rain is transformed into kinetic energy. B. The buckets continue to rotate at constant angular velocity because the rain is falling vertically while the buckets move in a horizontal plane. C. The buckets slow down because the angular momentum of the bucket + rain system is conserved. D. The buckets continue to rotate at constant angular velocity because the total mechanical energy of the bucket + rain system is conserved. E. None of the above. © 2017 Pearson Education, Inc. Slide 12 -23