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CHAPTER 5 HW Part 1– WORK, ENERGY AND POWER Work p. 160-163 (W = Flld or W = Fdcosθ, where θ is the angle between F and d) 1. A toddler pushes a cart across a floor with a force of 32 N parallel to the floor for a distance of 1.5 m. If the baby pushes the cart at a constant velocity, how much work was done by: a) the baby b) friction c) total? 2. A person slides a 102 kg crate 15.0 m across a level floor at a constant speed. The coefficient of kinetic friction is 0.20. How much work was done by a) the person b) friction c) total? 3. It takes 350 J to move a box 10 m along a flat surface. What force parallel to the motion was applied? 4. A sled is pulled over level snow for a distance of 0.500 km by a force of 124 N applied to a rope that makes an angle of 35.0° with the surface. How much work has been done by this force? 5. A person pulls a loaded sled by a rope that makes an angle 45° with the horizontal. The loaded sled is 60.0 kg and the sled is pulled a distance of 1.00 km. If the tension in the rope is 16.3 N and force due to kinetic friction is 11.5 N, then how much work was done by each force? (Consider all four forces) 6. A person lifts a 2.5 kg package to a height of 2.2 m. How much work was done by: a) the person? b) gravity? c) What is the total work? 7. A person lowers a 2.5 kg package from a height of 2.2 m. How much work was done by: a) the person? b) gravity? c) What is the total work? 8. The third floor of a building is 10 m above the ground floor and the tenth floor is 35 m above the ground floor. If 3.2 x 105 J of work is necessary to lift the elevator from the 3rd to 10th floor, what is the mass of the elevator? 9. A loaded trunk has a mass of 35 kg. The coefficient of friction between the trunk and the floor is 0.20. How much work is done on the trunk by a person who slides the trunk 8.0 m across a level floor then lifts it into a truck 1.3 m above the level of the floor? Kinetic and Potential Energy p. 164 – 172 and p. 179 – 181 (KE = 1/2 mv2, Ug = mgh, Wnet = KE = ½ m v2, P = W/t) 10. How does the kinetic energy of an object change when its mass is a) doubled b) cut to one-forth its original mass? How does the kinetic energy of an object change when its velocity is a) tripled b) cut in half c) cut to oneeight its original velocity? 11. What is the kinetic energy of a 1200 kg car traveling at 25 m/s? 12. How fast must a 12 kg toddler crawl if it has kinetic energy of 24 J? 13. An electron, which has a mass of 9.1 x 10-31 kg, is moving with a kinetic energy of 4.1 x 10-16 J. What is its velocity? 14. What is the potential energy of the package in problem 6 when it is: a) resting on the ground b) at the height of 2.2 m? 15. A 75 kg skier skies from an elevation of 2350 m to 1500 m. Given that his potential energy at 1500 m is zero, what is his potential energy at 2350 m? 16. The work energy theorem states that it takes a certain amount of work to get an object to change its velocity. If an objects kinetic energy is 5.0 J, how much work will be necessary to get the object to: a) double its velocity b) cut its velocity to one-third its original c) increase its velocity ten-fold? 17. How much work does a car engine do accelerating a 920 kg car from 0 to 35 m/s? 18. How much work do the breaks of a 920 kg car do in slowing it down from 25 km/hr to 0 km/hr? 19. An outfielder throws a 250 g baseball with an initial speed of 18 m/s. An infielder at the same level catches the ball when the speed is reduced to 12 m/s. How much work was done on the ball by air resistance? 20. What power is required to raise a 47 kg mass to a height of 12 m in 15 s? 21. How many times more power is required to change the velocity of a car by the following amounts: a) double the velocity b) cut the velocity in half c) triple the velocity d) decrease the velocity to one-forth its original? 22. How many kilowatts are required to raise a 2.50 x 103 kg loaded elevator to a height of 50.0 m in 10.0 s?