Unit 3 Practice Problems - Worksheet Chapters 5 and 6 A...

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Worksheet: Chapters 5 and 6 A small magnet is pulled up into the air toward a larger magnet fixed to the ceiling. The small magnet gains 10 J of kinetic energy and 20 J of gravitational potential energy. Careful temperature readings show that the process produces 0.5 J of heat energy. 1) How much work was done on the small magnet? Answer: 10 J 2) How much work was done on the small magnet-earth gravitational system? Answer: 20 J 3) How much work was done to randomly accelerate the atoms of the magnets? Answer: 0.5 J 4) How much work was done by the magnetic forces between the magnets? Answer: 30.5 J A cannon fires a 10-kg projectile at an initial velocity of 100 m/s [N60°U]. Use the Law of Conservation of Energy to solve the following problems. Confirm your answers using the methods from Chapter 3. 5) What is the speed of the projectile when it is at an altitude of 200 m? Answer: 78.0 m/s 6) How much work has been done on the projectile by the time it is at an altitude of 200 m? Answer: -1.96 x 10 4 J = -19.6 kJ 7) What is the altitude of the projectile when it has a speed of 60 m/s? Answer: 3.26 x 10 2 m 8) How much work has been done by gravity by the time the projectile has a speed of 60 m/s? Answer: -3.19 x 10 4 J = -31.9 kJ 9) What information was irrelevant when you solved the questions above? Answer: The direction of the projectile’s motion. A 5-kg box on a tabletop is connected by a massless wire to a second box suspended from a massless and frictionless pulley, as shown below. The tabletop has a coefficient of kinetic friction k = 0.25. 10) What is the speed of the boxes when the box on the table has moved 1.5 meters? Answer: 3.32 m/s 11) How much work has been done on one of the boxes when the box on the table has moved 1.5 meters? Answer: 27.6 J 12) How much work has been done by gravity when the box on the table has moved 1.5 meters? Answer: 73.5 J 13) How far has the box on the table moved at the instant friction has produced 20 J of heat? Answer: 1.63 m 14) What is the speed of the boxes at the instant that heat is being produced at a rate of 65 W? Answer: 5.31 m/s k = 0.25 5 kg 5 kg
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A marble of mass m = 15 grams slides down a frictionless ramp of height h = 2.0 m to the bottom of a circular loop of radius r = 0.60 m, as shown at right. 15) What is the speed of the marble when it reaches the bottom of the ramp? 6.26 m/s 16) What normal force does the loop exert on the marble once it reaches the curved section at the bottom of the loop? 1.13 N 17) What is the speed of the marble at the instant it reaches the top of the loop? 3.96 m/s 18) What normal force acts on the marble at the instant it reaches the top of the loop? 0.245 N 19) From what minimum height h could the marble be released and still travel completely around the loop? 1.50 m A 50-kg mass is released from rest and begins to slide from the top of the incline shown at right.
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