Irina Lyublinskaya, Gregg Wolfe, Douglas Ingram , Liza Pujji
ISBN #9781938168932
2,282 Questions
Homework Questions
This chapter emphasizes that work is the transfer of energy when a force acts over a displacement, and introduces the work-energy theorem which relates net work to changes in kinetic energy. It distinguishes between conservative forces, which allow energy to be stored as potential energy (gravitational or elastic), and nonconservative forces, which often convert mechanical energy into thermal energy. The concept of power is presented as the rate of energy transfer, and practical applications range from everyday human activities to large-scale energy consumption. Overall, the conservation of energy remains a central theme, with an emphasis on efficiency and the inevitable losses when not all energy is converted into useful work.
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How much work does a supermarket checkout attendant do on a can of soup he pushes 0.600 m horizontally with a force of 5.00 N? Express your answer in joules and kilo calories.
A 75.0-kg person climbs stairs, gaining 2.50 meters in height. Find the work done to accomplish this task.
(a) Calculate the work done on a 1500-kg elevator car by its cable to lift it 40.0 m at constant speed, assuming friction averages 100 N. (b) What is the work done on the lift by the gravitational force in this process? (c) What is the total work done on the lift?
Suppose a car travels 108 km at a speed of 30.0 m/s, and uses 2.0 gal of gasoline. Only 30% of the gasoline goes into useful work by the force that keeps the car moving at constant speed despite friction. (See Table 7.1 for the energy content of gasoline.) (a) What is the magnitude of the force exerted to keep the car moving at constant speed? (b) If the required force is directly proportional to speed, how many gallons will be used to drive 108 km at a speed of 28.0 m/s?
Calculate the work done by an 85.0-kg man who pushes a crate 4.00 m up along a ramp that makes an angle of $20.0^{\circ}$ with the horizontal. (See Figure 7.35.) He exerts a force of 500 N on the crate parallel to the ramp and moves at a constant speed. Be certain to include the work he does on the crate and on his body to get up the ramp.