Tipler 6e Clicker Questions Chapter 5

Chapter 5: Applications of Newton's Laws

1. Section: 5-1 Topic: Friction Type: Conceptual Four identical blocks are moving on a surface for which the coefficient of kinetic friction between each block and the surface is µk. The velocity of each block is indicated by the vector on the block. For which block is the force of friction between the surface and the block greatest? A) 1 B) 2 C) 3 D) 4 E) The force of friction is the same for all blocks. Ans: E 2. Section: 5-1 Topic: Friction Type: Conceptual A block of mass m is at rest on an inclined plane that makes an angle of 30º with the horizontal, as shown in the figure. Which of the following statements about the force of static friction is true? A) fs > mg D) fs = mg sin 30º B) fs > mg cos 30º E) None of these statements is true. C) fs = mg cos 30º Ans: D 3. Section: 5-1 Topic: Friction Type: Challenge Two objects are sliding at the same speed across a wooden surface. The coefficient of kinetic friction between the first object and the surface is twice that between the second object and the surface. The distance traveled by the first object before it stops is S. The distance traveled by the second object is A) impossible to determine without knowing the masses involved. B) 2S C) S/2 D) S E) 4S Ans: B 4. Section: 5-1 Topic: Friction Type: Conceptual A worker pulls horizontally on a rope that is attached to a 10-kg crate resting on a rough floor. The coefficients of static and kinetic friction are 0.5 and 0.3, respectively. The worker pulls with a force of 40 N. The frictional force exerted by the surface is A) 30 N B) 50 N C) 10 N D) 100 N E) 40 N Ans: E

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Chapter 5: Applications of Newton's Laws

5. Section: 5-1 Topic: Friction Type: Conceptual A heavy truck and a light car are traveling at the same speed on the same roadway. If the coefficients of static friction between their tires and the road are the same, which vehicle will be able to stop in the shortest distance? Assume both vehicles can apply their brakes with the maximum static friction force. A) the car B) the truck C) Both will be able to stop in the same distance. D) One cannot tell without knowing their coefficients of kinetic friction. E) One cannot tell without knowing their masses. Ans: C 6. Section: 5-1 Topic: Friction Type: Conceptual Which fundamental force(s) gives rise to friction? A) gravitational force D) strong nuclear force B) electromagnetic force E) (A) and (B) C) weak nuclear force Ans: B 7. Section: 5-1 Topic: Friction Type: Reading Which of the following statements is NOT true about friction? A) µk is less than µs. B) µk is independent of the relative speed of the surfaces in the range of about 1 cm/s to several meters per second. C) µk depends on the relative speed of the surfaces at speeds over several meters per second. D) The coefficients of friction depend on the nature of the surfaces. E) The force of static friction depends on the area of contact between the two surfaces. Ans: E 8. Section: 5-1 Topic: Friction Type: Conceptual A block of wood is pulled by a horizontal string across a rough surface at a constant velocity with a force of 20 N. The coefficient of kinetic friction between the surfaces is 0.3. The force of friction is A) impossible to determine without knowing the mass of the block. B) impossible to determine without knowing the speed of the block. C) 0.3 N D) 6 N E) 20 N Ans: E

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Chapter 5: Applications of Newton's Laws

9. Section: 5-1 Topic: Friction Type: Conceptual A mass m is placed on a rough incline at an F angle θ to the horizon. A force F is applied up the incline, to prevent the mass from sliding m down the incline, and it is just enough to θ prevent the mass from sliding down the incline. Using the compass rose, the direction of the frictional force is along A) (a) D) (d) B) (b) E) (e) C) (c) Ans: B 10. Section: 5-1 Topic: Friction Type: Conceptual A mass m is placed on a rough incline at an F angle θ to the horizon. A force F is applied up the incline so that the mass slides up the incline. m Using the compass rose, the direction of the θ frictional force is along A) (a) B) (b) C) (c) Ans: D

D) E)

a b d e

c

a b d e

c

(d) (e)

11. Section: 5-1 Topic: Friction Type: Conceptual A block of mass m is pulled in the direction shown in the figure across a rough surface. The magnitude of the frictional force is A) µkmg Ans: E

B) µkT cos θ

C) µk(T – mg)

D) µkT sin θ

12. Section: 5-1 Topic: Friction Type: Conceptual A block of mass m is pulled in the direction shown in the figure across a rough surface with a constant r acceleration a . The magnitude of the frictional force is A) µkmg B) T cos θ – ma C) µk(T – mg) D) µkT sin θ Ans: B 13. Section: 5-1 Topic: Friction Type: Reading The SI units for the coefficient of friction are A) newtons per meter. B) meters. C) newtons. D) newtons times meters.

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E) µk(mg – T sin θ )

E) µk(mg + sin θ )

Chapter 5: Applications of Newton's Laws

E) None of these is correct; the coefficient of friction is dimensionless. Ans: E 14. Section: 5-1 Topic: Friction Type: Numerical r A horizontal force F is used to push an object of mass m up an inclined plane. The angle between the plane and the horizontal is θ . The normal reaction force of the plane acting on the mass m is A) mg cos θ + F cos θ B) mg cos θ C) mg cos θ + F sin θ D) mg cos θ – F cos θ E) impossible to determine because the coefficient of friction is not given. Ans: C 15. Section: 5-1 Topic: Friction Type: Conceptual Two blocks connected by a string over a pulley are moving with constant speeds v up and down two connected stationary ramps, A and B, as shown. The blocks will accelerate if A) angle β is increased while α is held constant. B) angle α is increased while β is held constant. C) the coefficient of friction µk for surface A is increased. D) the coefficient of friction µk for surface B is increased. Ans: A 16. Section: 5-1 Topic: Friction Type: Conceptual The blocks shown in the figures have equal masses and are made of the same material. The velocity is the same in each figure. The total frictional force exerted by the surface on the blocks is

A) greater in Figure C than in Figure A or Figure B. B) the same in Figure C as in Figure A. C) the same in Figures A, B, and C. D) the same in Figure A and Figure B. E) the same in Figure C and Figure B. Ans: E

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Chapter 5: Applications of Newton's Laws

17. Section: 5-1

Topic: Friction

Type: Conceptual

Which free-body diagram best represents the forces acting on the student at rest on the incline?

Ans: E 18. Section: 5-1

Topic: Friction

Type: Conceptual

Which free-body diagram best represents the forces acting on the student sliding down a rough incline?

Ans: E 19. Section: 5-1 Topic: Friction Type: Calculation A block of mass M is sliding down a rough inclined surface that makes an angle θ with respect to the horizontal. If the coefficient of static friction is µ s and kinetic friction is µ k, then the acceleration of the block down the incline is equal to A) gsin θ − g µ s × cos θ D) gsin θ − g µ k × cos θ B) Gcos θ − g µ k × cos θ E) gsin θ − g µ s × cos θ − g µ k × cos

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Chapter 5: Applications of Newton's Laws

θ

C) g µ s × cos θ − gsin θ Ans: D

20. Section: 5-2 Topic: Drag Forces Type: Reading In drag racing, the driver deploys a parachute at the end of the ¼ mile run. The parachute works well because A) the dragster does not have any brakes to save weight. B) the drag force due to the parachute is large at high speeds. C) there is no rolling friction at high speeds. D) the driver has no time to apply the brakes. E) the deployment of the parachute is part of the show. Ans: B 21. Section: 5-2 Topic: Drag Forces Type: Conceptual If a jet plane doubles the speed, the drag force on the jet plane A) decreases by half. D) quadruples. B) is unchanged. E) depends how many passengers the plane is carrying. C) doubles. Ans: D 22. Section: 5-2 Topic: Drag Forces Type: Conceptual As a sky diver falls through the air, her terminal speed A) depends on her mass. B) depends on her body's orientation. C) depends on the local value of the acceleration due to gravity. D) depends on the density of the air. E) all of the above. Ans: E 23. Section: 5-3 Topic: Motion Along a Curved Path Type: Conceptual When a particle moves in a circle with constant speed, its acceleration is A) constantly increasing. D) constant in magnitude. B) constant in direction. E) constant in magnitude and direction. C) zero. Ans: D 24. Section: 5-3 Topic: Motion Along a Curved Path Type: Conceptual An object traveling in a circle at constant speed A) is moving with constant velocity. B) may be slowing down or picking up speed. C) experiences no acceleration. D) experiences an acceleration toward the center of the circle. E) none of the above Ans: D

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Chapter 5: Applications of Newton's Laws

25. Section: 5-3 Topic: Motion Along a Curved Path Type: Calculation A car going around a curve of radius R at a speed V experiences a centripetal acceleration ac. What is its acceleration if it goes around a curve of radius 3R at a speed of 2V? A) (2/3)ac B) (4/3)ac C) (2/9)ac D) (9/2)ac E) (3/2)ac Ans: B 26. Section: 5-3 Topic: Motion Along a Curved Path Type: Conceptual A car experiences both a centripetal and a tangential acceleration. For which of the following would this be true? A) It is going around a curve at a constant speed. B) It is going around a curve and slowing down. C) It is going along a straight road at a constant speed. D) It is going along a straight road and increasing its speed. E) It is going along a straight road and decreasing its speed. Ans: B 27. Section: 5-3 Topic: Motion Along a Curved Path Type: Conceptual The figure shows a top view of a ball on the end of a string traveling counterclockwise in a circular path. The speed of the ball is constant. If the string should break at the instant shown, the path that the ball would follow is

A) 1 B) 2 Ans: B

C) 3

D) 4

E) impossible to tell from the given information.

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Chapter 5: Applications of Newton's Laws

28. Section: 5-3 Topic: Motion Along a Curved Path The figure shows a top view of a ball on the end of a string traveling counterclockwise in a circular path. Assume that air resistance is negligible. Which free-body diagram best represents the net force acting on the ball?

Type: Conceptual

Ans: D 29. Section: 5-3 Topic: Motion Along a Curved Path The figure shows a top view of a ball on the end of a string traveling counterclockwise in a circular path. Assume that air resistance is negligible. Which vector best represents the acceleration of the ball?

Ans: D

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Type: Conceptual

Chapter 5: Applications of Newton's Laws

30. Section: 5-3 Topic: Motion Along a Curved Path A block slides down a frictionless incline. The path at the bottom of the incline is an arc of a circle. The direction of the net force on the block at the bottom of the arc (point P) is along (use the compass rose)

Type: Conceptual

a b c

e d P

A) B) C) Ans:

(a) (b) (c) A

D) (d) E) (e)

31. Section: 5-3 Topic: Motion Along a Curved Path Type: Conceptual c A ball of mass m is attached to a thin string and whirled in a vertical circle or radius r. The tension in d b the string at point e where the ball is moving with speed v is r a

e

A) B) C) Ans:

D) mv2/r E) none of the above.

mg mg – mv2/r mg + mv2/r D

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f

Chapter 5: Applications of Newton's Laws

32. Section: 5-3 Topic: Motion Along a Curved Path Type: Conceptual c A ball of mass m is attached to a thin string and whirled in a vertical circle or radius r. The tension in d b the string at point c where the ball is moving with speed v is r a

e

A) B) C) Ans:

D) mv2/r E) none of the above.

mg mg – mv2/r mg + mv2/r B

f

33. Section: 5-3 Topic: Motion Along a Curved Path Type: Conceptual c A ball of mass m is attached to a thin string and whirled in a vertical circle or radius r. The tension in d b the string at point f where the ball is moving with speed v is r a

e

A) B) C) Ans:

2

mg mg – mv2/r mg + mv2/r C

D) mv /r E) none of the above.

f

34. Section: 5-5 Topic: The Center of Mass Type: Conceptual When you accelerate your car, the front of the car lifts up slightly. When you brake, the front dips down. The primary reason is because the A) center of mass of the car and its contents are below the center of the wheel. B) center of mass of the car and its contents are above the center of the wheel. C) center of mass of the car and its contents are at the center of the wheel. D) center of mass of the car and its contents are above the road. E) car has inertia. Ans: D

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Chapter 5: Applications of Newton's Laws

35. Section: 5-5 Topic: The Center of Mass Type: Numerical A barbell is 1.5 m long. Three weights, each of mass 20 kg, are hung on the left, and two weights of the same mass are hung on the right. The width of each weight is 4 cm and the outside edge of each group of weights is placed 4 cm from the ends. Where is the center of mass of the barbell as measured from the mid-point, M, of the bar? The bar is of uniform mass and has mass 5 kg, and the retaining collars are of negligible mass. Take to the right as positive.

M

1.5 m A) -5.90 cm B) -5.62 cm C) +5.62 cm Ans: B

D) +5.90 cm E) None of the above

36. Section: 5-5 Topic: The Center of Mass Type: Conceptual A uniform horizontal bar is in a region of space where the acceleration due to gravity g varies, increasing from left to right. Where is the location of the center of mass relative to the center of gravity? A) They are at the same location. B) The center of mass is to the left of the center of gravity. C) The center of gravity is to the left of the center of mass. D) It depends on the shape of the bar. E) It depends on how much g changes. Ans: B Use the figure below for the next two problems. A mass, m1, attached to a spring is placed on a cart with mass m2, which moves freely and without friction on a table. m1 slides without friction on the cart and is ¼ the mass of m2. m1 frictionless

m2

37. Section: 5-5 Topic: The Center of Mass Type: Conceptual When m1 is allowed to oscillate along m2, what is the motion of m2? A) m2 does not move. B) m2 moves in the same direction as m1. C) m2 moves in the opposite direction of m1.

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Chapter 5: Applications of Newton's Laws

D) Depends on the spring constant. E) None of the above. Ans: C 38. Section: 5-5 Topic: The Center of Mass Type: Conceptual When m1 moves with a displacement of 1 cm in the +x direction, what is the displacement of m2? A) m2 does not move. B) m2 moves ¼ cm in the +x direction C) m2 moves 1 cm in the +x direction. D) m2 moves ¼ cm in the -x direction E) m2 moves 1 cm in the -x direction. Ans: D 39. Section: 5-5 Topic: Center of Mass Type: Conceptual The picture on the right shows an exploding firework high up in the air, just after the firework has come to a rest. Which point best describes the center of mass of the explosion?

Picture by H.K. Ng

A) a Ans: C

B)

b

C)

c

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D)

d

E) e