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(njk359) kodeih HW 6 Coker (56625) This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page nd all choices before answering. Homework on Chapter 7, which introduces the concepts of work, kinetic energy, gravitational potential energy, conservation of energy, and inclusion of nonconservative forces such as friction in using energy concepts. A lot of stu! 001 10.0 points An object with mass M is attached to the end of a string and is being lowered vertically at a g constant acceleration of . 4 If it has been lowered a distance from rest, how much work has been done by the tension in the string? 1. M g 4 3M g 2. 4 M g 3. 2 M g 4. 2 Answer in units of J. 1 003 (part 2 of 4) 10.0 points Find the work done by the normal force exerted by the table. Answer in units of J. 004 (part 3 of 4) 10.0 points Find the work done by the force of gravity. Answer in units of J. 005 (part 4 of 4) 10.0 points Find the work done by the net force on the block. Answer in units of J. 006 10.0 points An applied force varies with position according to F = k1 xn k2 , where n = 3, k1 = 4.7 N/m3 , and k2 = 66 N. How much work is done by this force on an object that moves from xi = 5.77 m to xf = 26.7 m? Answer in units of kJ. 007 10.0 points Moe, Larry and Curley are hard at work. Moe is carrying a 100 kg box 10 m horizontally across a room. Larry is lifting a 100 kg box from the oor to a shelf 2 m above the oor. Curley is climbing a ladder, to enter a hole in the ceiling 4 m above the oor. Which of the Stooges is doing work as dened in physics by W = F dr? 5. M g 6. M g M g 4 3M g 8. 4 7. 002 (part 1 of 4) 10.0 points A block of mass 2.11 kg is pushed 1.23 m along a frictionless horizontal table by a constant 16 N force directed 20 below the horizontal. 1. Moe and Larry are doing work; Curley is doing no work. 2. Moe is doing work; Larry and Curley are doing no work. 3. Moe and Curley are doing work; Larry is doing no work. 4. Larry and Curley are doing work; Moe is doing no work. 5. Larry is doing work; Moe and Curley are 16 N 2.11 kg =0 20 Find the work done by the applied force. kodeih (njk359) HW 6 Coker (56625) doing no work. 6. Curley is doing work; Moe and Larryy are doing no work. 008 10.0 points A force F of magnitude 2x3 is applied to stop a particle moving with an initial velocity v0 . The particle travels from x = 0 to x = D in coming to a stop after the force F is applied. The work done by F is 1 1. D3 2 1 2. D4 2 3. D4 4. 2D3 1 5. D3 2 1 6. D4 2 7. D4 8. D3 009 10.0 points An amount of work W is done on an object of mass m initially at rest, and as result it winds up moving at speed v . Suppose instead it were already moving at speed v and the same amount of work W was done on it. What would be its nal speed? 1. zero; the new work would always cancel the eect of the original work. 2. still v 3. 2 v 4. 2 v 5. 4 v 010 10.0 points 2 Two identical objects are moving directly toward one another at the same speed v . m v v m What is the total kinetic energy of the system of the two objects? 1. m v 2 since energy is a scalar 2. 4 m v 2 since (2 v )2 = 4 v 2 3. Zero since (v v)2 = 0 4. None of these 1 5. Still m v 2 from the denition of kinetic 2 energy 011 10.0 points A student in Denver (altitude = 1 mile = 1609 m above sea level) brings a physics book of mass 1.2 kg to the top of a ten story building of height 34 m and holds the book over her head 127 cm above the roof. What is the gravitational potential energy Ug of book? the 1. Ug = 0 J 2. Ug = 19356.3 J 3. Ug = 14.9504 J 4. Cannot be determined 5. Ug = 415.198 J 012 (part 1 of 2) 10.0 points A rock of mass m is thrown horizontally o a building from a height h. The speed of the rock as it leaves the throwers hand at the edge of the building is v0 as shown. kodeih (njk359) HW 6 Coker (56625) v0 A 8m h 22.8 m 3 x How much time does it take the rock to travel from the edge of the building to the ground? 1. t = 2h g h 2. t = v0 3. t = 4. t = 5. t = h v0 h v0 g 2h g What is its speed at point A ? Answer in units of m/s. 015 10.0 points A roller coaster cart of mass m = 387 kg starts stationary at point A, where h1 = 22.9 m and a while later is at B , where h2 = 12.7 m. The acceleration of gravity is 9.8 m/s2 . A B h1 h2 013 (part 2 of 2) 10.0 points What is the kinetic energy of the rock just before it hits the ground? 1 2 1. Kf = m v0 m g h 2 2. Kf = m g h 1 2 m v0 + m g h 2 1 2 4. Kf = m v0 2 1 2 5. Kf = m g h m v0 2 3. Kf = 014 10.0 points A bead slides without friction around a loopthe-loop. The bead is released from a height of 22.8 m from the bottom of the loop-theloop which has a radius 8 m. The acceleration of gravity is 9.8 m/s2 . What is the speed of the cart at B , ignoring the eect of friction? Answer in units of m/s. 016 10.0 points Note: The pendulum bob is released at a height below the height of the peg. A pendulum made of a string of length 11.7 m and a spherical bob of mass 9.2 kg and negligible raius swings in a vertical plane. The pendulum is released from an angular position 41 from vertical as shown in the gure below. The string hits a peg located a distance 7 m below the point of suspension and swings about the peg up to an angle on the other side of the peg. Then, the bob proceeds to oscillate back and forth between these two angular positions. The acceleration of gravity is 9.8 m/s2 . kodeih (njk359) HW 6 Coker (56625) 5. Wnet = (f m g )H . 7m 6. Wnet = (m g f )H . 4 m 9.2 kg 41 9.8 m/s2 What is the maximum angle which the pendulum will swing to the right after hitting the peg as shown above? Answer in units of . 017 10.0 points A block of mass 3.1 kg, sliding on a horizontal plane, is released with a velocity of 3.2 m/s. The blocks slides and stops at a distance of 1.9 m beyond the point where it was released. How far would the block have slid if its initial velocity were quadrupled? 1. 60.8 m 2. 1.9 m 3. 7.6 m 4. 30.4 m 5. 15.2 m 6. 3.8 m 018 10.0 points A piece of paper of mass m is dropped from a height H , to the oor (height = 0). The force of air friction has magnitude f . The net work Wnet done on the paper is 1. Wnet = m g H . 2. Wnet = f H . 3. Wnet = f H . 4. Wnet = m g H . 019 10.0 points A block of mass m is pushed a horizontal distance D from position A to position B, along a horizontal plane with friction coecient . Then m is pushed from B to A. If the force pushing m from A to B is P , and the force pushing m from B to A is P , what is the total work done by friction? 1. 2 ( m g P ) D 2. +2 m g D 3. 2 (P m g ) D 4. 0 5. 2 m g D 020 10.0 points Starting from rest at a height equal to the radius of the circular track, a block of mass 24 kg slides down a quarter circular track under the inuence of gravity with friction present (of coecient ). The radius of the track is 38 m. The acceleration of gravity is 9.8 m/s2 . 24 kg 11 .7 38 m If the kinetic energy of the block at the bottom of the track is 3400 J, what is the work done against friction? Answer in units of J. ... View Full Document

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