Physics 53 Exam 3 November 3, 2010 Dr. Alward

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Aileen Copeland
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1 1. When the speed of a rear-drive car (a car that's driven forward by the rear wheels alone) is increasing on a horizontal road the direction of the frictional force on the tires is: A) forward for all tires B) backward for all tires C) forward for the front tires and backward for the rear tires D) backward for the front tires and forward for the rear tires 2. A wheel is spinning at 27 rad/s but is slowing with an angular acceleration that has a magnitude given by 3.0 t 2, in rad/s 2. The wheel stops in a time of: A) 1.7 s B) 2.6 s C) 3.0 s D) 4.4 s 3. A wheel initially has an angular velocity of 18 rad/s. It has a constant angular acceleration of 2.0 rad/s 2 and is slowing. Through how many radians will the wheel have turned by the time its angular velocity is10 rad/s? A) 112 B) 96 C) 144 D) A rod is pivoted about its center. A 5-N force is applied 4 m from the pivot and another 5-N force is applied 2 m from the pivot, as shown. The magnitude of the total torque about the pivot (in N m) is: A) 0 B) 5 C) 8.7 D) 15 Page 1

2 5. A hoop (I = MR 2 ), a uniform disk (I = MR 2 /2), and a uniform sphere (I = 2MR 2 /5), all with the same mass M and outer radius R, start with the same speed and roll without sliding up identical inclines. Rank the objects according to how high they go, least to greatest. A) hoop, disk, sphere B) disk, hoop, sphere C) sphere, hoop, disk D) sphere, disk, hoop 6. When a thin uniform stick of mass M and length L is pivoted about its midpoint, its rotational inertia is ML 2 /12. When pivoted about a parallel axis half-way between one end and the center of the rod, its rotational inertia is: A) 3ML 2 /28 B) 7ML 2 /48 C) 5ML 2 /36 D) 7ML 2 /24 7. A 5.0-kg block starts from rest at the origin and thereafter has an acceleration given by a = <4, 2> in m/s 2.The torque (in N-m), relative to the origin, acting on it at the end of 3.0 s is: A) <16, 0, 48> B) <18, 0, 0> C) <0, 0, 144> D) <0, 0, 108> 8. A uniform sphere of radius R rotates about a diameter with kinetic energy K 0 and angular momentum L 0. Under the action of internal forces the sphere collapses to a uniform sphere of radius R/2. Its new kinetic energy is: A) K 0 /4 B) 2K 0 C) 4K 0 D) 16K 0 Page 2

3 9. A wheel,with rotational inertia I, mounted on a vertical shaft with negligible rotational inertia, is rotating with angular speed 0. A non-rotating wheel with rotational inertia 2I is dropped onto the same shaft as shown.. The resultant combination of the two wheels and shaft will rotate at: A) 0 /2 B) 2 0 C) 0 /3 D) A uniform 240-gram meter stick can be balanced by a 240-gram mass placed at the 100- cm mark if the fulcrum is placed at the point marked: A) 75 cm B) 60 cm C) 50 cm D) 40 cm 11. An 800-N man stands halfway up a uniform 5.0 m ladder weighing 200 N. The base of the ladder is 3.0 m from the wall as shown. Assuming that the wall-ladder contact is frictionless, the wall pushes against the ladder with a force of: A) 250 N B) 325 N C) 375 N D) 600 N Page 3

4 12. A 240-N weight is hung from two ropes as shown. The tension in the rope slanting upward to the right has magnitude: A) 0 B) 656 N C) 480 N D) 416 N 13. A picture can be hung on a wall in three different ways, as shown. The tension in the string is: A) least in I B) greatest in I C) greatest in II D) least in III E) greatest in III 14. A 160-N child sits on a light swing and is pulled back and held with a horizontal force of 100 N. The magnitude of the tension force of each of the two supporting ropes is: A) 60 N B) 94 N C) 120 N D) 190 N Page 4

5 15. A wheel starts from rest and has an angular acceleration of 4.0 rad/s 2. The time it takes to make 10 revolutions is: A) 5.6 s B) 0.71 s C) 2.2 s D) 2.8 s 16. A cube with 2.0-m sides is made of material with a bulk modulus of N/m 2. When it is submerged in a fluid that subjects it to a pressure of Pa the length in m of its any of its any of its sides is: A) 1.85 B) 1.95 C) 1.66 D) Let M denote the mass of uniform planet and let R denote its radius. What is the acceleration due to gravity at an altitude of 4R, given as a multiple of the acceleration due to gravity on the planet's surface? Note: altitudes are measured from the surface of the Earth. A) 1/4 B) 1/16 C) 1/25 D) 1/9 18. A projectile is fired straight upward from Earth's surface with a speed that is half the escape speed. Assume the speed that's reached occurs near the surface of the Earth. If R is the radius of Earth, the highest altitude reached, measured from the surface, is: A) R/4 B) R/3 C) R/2 D) R Page 5

6 19. Each of the four corners of a square with edge a is occupied by a point mass m. There is a fifth mass, also m, at the center of the square. To remove the mass from the center to a point far away the work that must be done by an external agent is given by: A) 4Gm 2 /a B) 4Gm 2 /a C) Gm / a D) Gm / a 20. The mass of a hypothetical planet is 1/100 that of Earth and its radius is 1/4 that of Earth. If a person weighs 600 N on Earth, what would he weigh on this planet? A) 24 N B) 48 N C) 96 N D) 192 N Page 6

7 Answer Key 1. D 2. C 3. D 4. D 5. A 6. B 7. D 8. C 9. C 10. A 11. C 12. C 13. E 14. B 15. E 16. C 17. C 18. B 19. C 20. C Page 7

Webreview Torque and Rotation Practice Test

Webreview Torque and Rotation Practice Test Please do not write on test. ID A Webreview - 8.2 Torque and Rotation Practice Test Multiple Choice Identify the choice that best completes the statement or answers the question. 1. A 0.30-m-radius automobile