The second image has the background info used to solve the practice problem Page 112 Practice Problem 4.9: Suppose that the elevator is accelerating downward at2.00m/s². What does the scale read during the acceleration? Answer: 478 N. 114 CHAPTER 4 Newton's Laws of MotionEXAMPLE 4.9 Weighing yourself in an elevatorIn our final example in this chapter we will analyze the forces acting on your body as you move in an eleva-tor. Specifically, we will consider the case where the elevator is accelerating. Suppose that you stand on abathroom scale that rests on the floor of an elevator. (Don't ask why!) Standing on the scale compresses itsinternal springs and activates a dial that indicates your weight in newtons. When the elevator is at rest, thescale reads 600 N. Then the elevator begins to move upward with a constant acceleration a, = 2.00 m/s².(a) Determine your mass. (b) Determine the scale reading while the elevator is accelerating. (c) If you readthe scale without realizing that the elevator is accelerating upward, what might you think your mass is?SOLUTIONSET UP All the forces are vertical; we take the y axis to be verticallyupward. We ignore the weight of the scale itself. When the scale isequilibrium (not accelerating), the total force acting on it must be zero.When it reads 600 N, forces of magnitude 600 N (with opposite direc-tions) are applied to its top and bottom surfaces. Using this analysis, wedraw separate free-body diagrams for you and the scale (Figure 4.28).SOLVE Part (a): At first, you, the scale, and the elevator are at rest in aninertial system; all three objects are in equilibrium. You push down on thescale with a force of magnitude 600 N, and (from Newton's third law) thescale applies an equal and opposite upward force to your feet. The onlyother force on you is your weight; you are in equilibrium, so the total ycomponent of force on you is zero. Your weight is 600 N, and your mass is600 N9.80 m/s²m =W8= 61.2 kg (about 135 lb).Part (b): When the system accelerates upward at 2.00 m/s², yourweight is still 600 N, but now the upward force the scale applies to yourfeet is different because you are no longer in equilibrium. We'll callthe magnitude of the upward force F (Figure 4.28b). We use Newton'ssecond law to relate the acceleration to the net force:F-600 N = ma = (61.2 kg)(2.00 m/s²)FREQUENTLY ASKED QUESTIONS600 N1600 Nand600 Nw = mg= 600 NAt equilibrium(a)A FIGURE 4.28 Our diagrams for this problem.w Tutor Solutionw=600 NAccelerating(b)F = 722 N.Part (c): If you think your weight is 722 N, then you are likely to con-clude that your mass is m = w/g = (722 N)/(9.8 m/s²) = 73.7 kg,instead of the actual value of 61.2 kg.lighter or heavier in an elevator. Do these feelings occur only when theREFLECT Relate what we've said here to your own feeling of beingelevator is accelerating?Practice Problem: Suppose that the elevator is accelerating downward at2.00 m/s². What does the scale read during the acceleration? Answer: 478 N.BridA 10 kg cin Figure19.6E(2) the co-(b) the maforce perSet UpChocDrauCalc• Wri•CHForc-(Sectmechan otor sNe(Seobis

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Description: The second image has the background info used to solve the practice problem Page 112 Practice Problem 4.9: Suppose that the elevator is accelerating downward at2.00m/s². What does the scale read during the acceleration? Answer: 478 N. 114 CHAPTER 4 N