Section 4.1 Review Understanding Concepts 1. a) What three conditions are nec- essary for work to be done? b) Define the joule. c) How much work is required to lift a 200-kg mass 2.0 m? 2. How much work is done by a foot- ball player pushing an opponent with a force of 700 N [E] for a dis- placement of 2.0 m [E]? 3. A child applies a force of 8.0 N [W] to pull a toy truck a displacement of 5.0 m [W] along the floor. How much work is done? 4. A plumber uses a rope to drag a heavy box 12 m across the shop. The rope makes an angle of 35 with the horizontal and the force applied is 280 N. How much work is done by the plumber? 5. A weightlifter lifts a 50-kg mass vertically 60 cm at constant veloc- ity and then lowers it back down in the same manner. Calculate the work done a) during the lift b) during the return Applying Inquiry/ Communication Skills 6. An archer obtains the force-stretch graph shown in Figure 4.14 for a bow. Calculate the work he did to stretch the bow 7.0 cm. Applied force F(N [backwards] 120 100 80 60 40 20 7. Three different forces are applied to an object, one after the other. The corresponding displacements are shown in Table 4.2. a) Calculate the work done by each force and the total work. b) Draw a force-position graph for the data. c) Calculate the total work using the graph. Compare this with the value obtained in a). TABLE 4.2 Force-Displacement Data Force Interval F(N [E]) Displacement Ad (m [E]) A 4.0 5.0 B 7.0 6.0 C 3.0 2.0 8. For a scientific inquiry into "work," a student wants to use a spring scale first to lift a wooden block up vertically and then to slide the block along a table. Outline the pro- cedure this student should use to set the zero on the spring scale in each part of the inquiry. 9. Prove that one joule is equivalent to 1 kg-m/s. Making Connections 10. Some people suggest that walking for 30 min on a treadmill two or three times a week is enough work to keep a person in good physical shape. What information would you need to find out if this is true? 0 2.0 4.0 6.0 8.0 10.0 12.0 Stretch displacement Ad(cm [back]) FIGURE 4.14