CHAPTER 6 TEST REVIEW ANSWER KEY SPHS Devil Physics

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6 I tie a rope to a 75 kg box so that I can pull it 25 meters across the floor The angle between the rope and. the ground when I am pulling is 30 If I pull with a force of 500N and friction is negligible. a How much work will I do, ANSWER a Only the component of the force in the x direction does work. b If it takes me 6 seconds to pull the box 25 meters how much power did I exert. ANSWER b Power is work divided by time,c What is the normal force acting on the box. ANSWER c The component of the pull force in the y direction lessens the normal force that. has to support the box, d If the coefficient of friction is 0 60 what is the work done by the friction force on the box. e Assuming the box was initially at rest what will be the velocity of the box at the end of the 25m. ANSWER e The work done on the box by pulling minus the work done on the box by. friction will result in an increase in kinetic energy. Chapter 6 Test Review Answers Updated 4 Feb 14 Page 2 of 7. f I now climb into the attic and use the rope to pull the box 3m to the attic at a constant rate How. much work did I do, g If it takes 8 seconds to pull the box into the attic how much power did I exert. ANSWER g Power is work divided by time,7 What is kinetic energy.
ANSWER The energy of motion, 8 Translational kinetic energy is directly proportional to the mass of an object and. it is proportional to the square of the speed of the object. 9 Explain the work energy principle, ANSWER The net work done on an object is equal to the change in its kinetic energy. 10 How much work is done by friction in keeping a 1000 kg box from sliding down a 12 incline if the. coefficient of friction is 0 36 the length of the ramp is 1 47m the temperature is 21 and the relative. humidity is 72 Oh and it s an odd numbered Tuesday. ANSWER None Since the box doesn t move there is no displacement and no change in kinetic energy so. no work is done,11 What is potential energy, ANSWER The energy associated with forces that depend on the position or configuration of a body or. bodies and the surroundings, Chapter 6 Test Review Answers Updated 4 Feb 14 Page 3 of 7. 12 What is the difference between gravitational potential energy and elastic potential energy. ANSWER Gravitational potential energy is caused by the gravitational attraction of the earth and the. body s position relative to the earth Elastic potential energy is always associated with a force that does. work on the elastic material and is equal and opposite to the work done by that force. 13 Define Hooke s law the spring equation and give the equation for elastic force and elastic potential. ANSWER Hooke s Law is where k is the spring constant and the negative sign is because the. force is in the opposite direction of the displacement x PEe 1 2kx2. 14 What is the difference between conservative and non conservative forces Give examples of each. ANSWER Conservative forces like gravity and springs do not depend on the path taken but only the. starting and ending points Non conservative forces like friction are calculated based on the total distance. covered and are thus dependent on the path taken, Lessons Learned for daily lives For conservatives the end always justifies the means and or path to get.
there no matter what you have to start with Non conservatives constantly rub you the wrong way no matter. how much you try to work around them, 15 Is mechanical energy conserved when friction is present Why or why not. ANSWER No Friction dissipates some of the mechanical energy in the form of heat. 16 State the law of conservation of energy and give the equation when gravity and friction are present. ANSWER The total energy is neither increased nor decreased in any process Energy can be transformed. from one form to another and transferred from one body to another but the total amount remains constant. 17 Define power, ANSWER The rate at which work is done or the rate at which energy is transformed. Chapter 6 Test Review Answers Updated 4 Feb 14 Page 4 of 7. 18 How much work is required to move a 150 kg box 17 m across a floor at a constant speed when the. coefficient of friction is 0 72, ANSWER According to Newton s Second Law F ma if there is no acceleration constant speed the. push force must equal the resistance force friction. 19 How much work would be required to push the same box 17 meters up an 11 incline with the same. coefficient of friction again at constant speed, ANSWER Here the work is equal to the change in potential energy plus the work done by friction to resist. the movement,Alternatively, The box is pushed 17m up the incline d which is the hypotenuse To find the elevation gain.
20 An M1 A1 Abrams battle tank fires a 10kg projectile with a muzzle velocity of 1575 m s How far will. it penetrate armour plating with a resistance force of 2 07x107N Assume the resistant force is constant. and the projectile hits perpendicular to the plating. ANSWER All of the kinetic energy of the projectile will be absorbed by the resistant force of the. Chapter 6 Test Review Answers Updated 4 Feb 14 Page 5 of 7. 21 The 1400 kg rocket Nissan Frontier has coil springs attached to each wheel with a spring constant of. 200 kN m each While jumping school buses the Frontier routinely reaches heights of 10m Assuming. it lands evenly on all four wheels weight evenly distributed how much does each spring initially. compress when it lands, ANSWER The potential energy of the Frontier at its highest point will be absorbed by the compression. of its springs Each spring will absorb 1 4th of the energy Note that 200 kN is equal to 2 0 x 105 N. 22 A 5000 kg school bus loses its brakes while travelling at 30 m s going downhill in the mountains It. veers off into a breakaway ramp with a 12 uphill incline filled with loose gravel It travels 25 m up the. incline before coming to a stop,a What was the retarding force of the gravel. ANSWER The work done by the gravity and the retarding force of the gravel absorbed all of the kinetic. energy of the school bus, b What was the retarding force acting on the students in the bus. ANSWER video games rap music CAS reflections and Twitter. Also accept non conservative forces and France, Chapter 6 Test Review Answers Updated 4 Feb 14 Page 6 of 7. 23 A 2500 kg rollercoaster is travelling at 2 5 m s at the top of a 45m drop At the bottom of the drop the. speed is measured to be 27 m s If the distance travelled was 65m what was the average resistant force. acting on the roller coaster, ANSWER At the top of the drop the roller coaster has PE and KE At the bottom of the drop the roller.
coaster only has KE but some of the original energy at the top has been dissipated through the work done by. resistant forces friction sound air resistance,PE1 KE1 KE2 WR. 24 How much power is required to accelerate the 1400 kg rocket Nissan Frontier from 50 km hr to 120. km hr in 6 sec Give your answer in ft lb s, ANSWER Work is done by the car s engine to change the car s kinetic energy Power is work divided. by time Use SI units to calculate work in watts and then convert to ft lb s. Bonus Which branch of the federal government constitutes the greatest dissipative force on the nation s. economy Justify Give examples, Chapter 6 Test Review Answers Updated 4 Feb 14 Page 7 of 7. Chapter 6 Test Review Answers Updated 4 Feb 14 Page 1 of 7 DEVVIIL PHHYYSSIICCSS BADDEESSTT OC CLLAA S SS ONN CAAMMPPUUS CHAPTER 6 TEST REVIEW ANSWER KEY 1 State the relationship between force work energy and power ANSWER Force is a mass under acceleration Work and energy are products of force and distance Power is work energy per unit

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