hmwk-3-Fall-2007 - PHY 317K September 27, 2007 HOMEWORK # 3...

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PHY 317K September 27, 2007 HOMEWORK # 3 DUE on October 10 by 8:00pm Instructions: Use a scantron ANSWER SHEET to mark answers. Provide your NAME (last, first), UTEID , and UNIQUE NUMBER of the course. Sign and date it. The answer sheets must be placed in the 317K box (by bulletin board outside PAI 2.48) by 8:00pm on Wednesday, October 10, 2006. Late homework will not be graded. 1. Which of the following groups does NOT contain a scalar quantity? A) velocity, force, power B) displacement, acceleration, force C) acceleration, speed, work D) energy, work, distance E) pressure, weight, time 2. An object moves in a circle at constant speed. The work done by the centripetal force is zero because: A) the displacement for each revolution is zero B) the average force for each revolution is zero C) there is no friction D) the magnitude of the acceleration is zero E) the centripetal force is perpendicular to the velocity 3. The work done by gravity during the descent of a projectile is: A) positive B) negative C) zero D) depends for its sign on the direction of the y axis E) depends for its sign on the direction of both the x and y axes Page 1
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4. A sled (including load) weighs 5000 N. It is pulled on level snow by a dog team exerting a horizontal force on it. The coefficient of kinetic friction between sledge and snow is 0.05. How much work is done by the dog team pulling the sledge 1000 m at constant speed? A) 2.5 × 10 4 J B) 2.5 × 10 5 J C) 5.0 × 10 5 J D) 2.5 × 10 6 J E) 5.0 × 10 6 J 5. A 1-kg block is lifted vertically 1 m by a boy. The work done by the boy is about: A) 1 ft lb B) 1 J C) 10 J D) 0.1 J E) zero 6. A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes an angle of 30 ° with the horizontal. His force is parallel to the slope. If the speed of the crate decreases at a rate of 1.5 m/s 2 , then the work done by the mand is: A) –200 J B) 61 J C) 140 J D) 200 J E) 260 J 7. An 80-N crate slides with constant speed a distance of 5.0 m downward along a rough slope that makes an angle of 30 ° with the horizontal. The work done by the force of gravity is: A) –400 J B) –200 J C) –69 J D) 200 J E) 400 J Page 2
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8. A block is attached to the end of an ideal spring and moved from coordinate x i to coordinate x f . The relaxed position is at x = 0. The work done by spring is positive if: A) x i = 2 cm and x f = 4 cm B) x i = –2 cm and x f = 4 cm C) x i = –2 cm and x f = –4 cm D) x i = 2 cm and x f = –4 cm E) x i = –4 cm and x f = –2 cm 9. An ideal spring, with a pointer attached to its end, hangs next to a scale. With a 100-N weight attached, the pointer indicates "40" on the scale as shown. Using a 200-N weight instead results in "60" on the scale. Using an unknown weight X instead results in "30" on the scale. The weight of X is: A) 10 N B) 20 N C) 30 N D) 40 N E) 50 N 10. When a certain rubber band is stretched a distance x , it exerts a restoring force of magnitude F = Ax , where A is a constant. The work done by a person in stretching this rubber band from x = 0 to x = L is: A) AL 2 B) A + 2 L C) A + 2 L 2 D) A / L E) AL 2 /2 Page 3
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11. An ideal spring is hung vertically from the ceiling. When a 2.0-kg mass hangs at rest from it the spring is extended 6.0 cm from its relaxed length. An upward external force
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hmwk-3-Fall-2007 - PHY 317K September 27, 2007 HOMEWORK # 3...

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