13. How much force must a locomotive exert on a 12,000-kg boxcarto make it accelerate forward at 0.4 m/s2? 14. How long will it take the boxcar in Problem 13 to reach itscruising speed of 100 km/h (62 mph or 28 m/s)? 15. The builders of the pyramids used a long ramp to lift 20,000-kg (22-ton) blocks. If a block rose 1 m in height while traveling 20 m along the ramp’s surface, how much uphill force was needed to push it up the ramp at constant velocity? P.15 9800 N. 16. How much work was done in raising one of the blocks inProblem 15 to a height of 50 m? 17. What is the gravitational potential energy of one of the blocks inProblem 15 if it’s now 75 m above the ground? 18. As water descends from the top of a tall hydroelectric dam, itsgravitational potential energy is converted to electric energy. Howmuch gravitational potential energy is released when 1000 kg ofwater descends 200 m to the generators? 19. The tire of your bicycle needs air so you attach a bicycle pump to it and begin to push down on the pump’s handle. If you exert a downward force of 25 N on the handle and the handle moves downward 0.5 m, how much work do you do? P.19 12.5 J. 20. You’re using a wedge to split a log. You are hitting the wedge with a large hammer to drive it into the log. It takes a force of 2000 N to push the wedge into the wood. If the wedge moves 0.2 m into the log, how much work have you done on the wedge? P.20 You have done 400 joules of work on the wedge. 21. The wedge in Problem 20 acts like a ramp, slowly splitting the wood apart as it enters the log. The work you do on the wedge, pushing it into the log, is the work it does on the wood, separating its two halves. If the two halves of the log only separate by a distance of 0.05 m while the wedge travels 0.2 m into the log, how much force is the wedge exerting on the two halves of the log to rip them apart? P.21 8000 N. 22. You’re sanding a table. You must exert a force of 30 N on thesandpaper to keep it moving steadily across the table’s surface. Youslide the paper back and forth for 20 minutes, during which time youmove it 1000 m. How much work have you done? 1. The chairs in an auditorium aren’t all facing the same direction. How could you describe their angular positions in terms of a reference orientation and a rotation? E.1 The angle by which the front, center seat would have to be rotated, as viewed from above, to have each seat’s orientation. 2. When an airplane starts its propellers, they spin slowly at first and gradually pick up speed. Why does it take so long for them to reach their full rotational speed?
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