# Trabajo y energia

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Tarea T14. Trabajo y energía
(Adaptada de Wilson, Buffa & Lou 2007, 6ª edición, Cap. 5) 7. CQ A jet plane flies in a vertical circular loop. In what regions of the loop is the work done by theplane’s weight positive and/or negative? Is the work constant? If not, are there maximum and minimum instantaneous values? Explain. A 3.00-kg block slides down a frictionless plane inclined 20° to thehorizontal. If the length of the plane’s surface is 1.50 m, how much work is done, and by what force? Suppose the coefficient of kinetic friction between the block and the plane in Exercise 12 is 0.275.What would be the net work done in this case? A hockey puck WITH a mass of 200 g and an initial speed of 25.0 m s

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slides freely to rest in the space of 100 m on a sheet ofhorizontal ice. How many forces do nonzero work on it as it slows: (a) (1) none, (2) one, (3) two, or (4) three? Explain. (b) Determine the work done by all the individual forces on the puck as it slows.19. A 500-kg, light-weight helicopter ascends from the ground with an 2 acceleration of 2.00 m s . Over a 5.00-s interval, what is (a) the work done by the lifting force, (b) the work done by thegravitational force, and (c) the net work done on the helicopter? To measure the spring constant of a certain spring, a student applies a 4.0-N force, and the spring stretches by 5.0 cm. What is thespring constant?

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43. CQ A certain amount of work W is required to accelerate a car from rest to a speed v. If instead an amount of work equal to 2W is done on the car, what is the car’s speed?50. IE A large car of mass 2m travels at speed v. A small car of mass m travels with a speed 2v. Both skid to a stop with the same coefficient of friction. (a) The small car will have (1) a longer, (2)the same, (3) a shorter stopping distance. (b) Calculate the ratio of the stopping distance of the small car to that of the large car. (Use the work–energy theorem, not Newton’s laws.) 51. An...