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Chapter 8: Q100P (page 211)
A swimmer moves through the water at an average speed of 0.22 m/s. The average drag force is 110 N. What average power is required of the swimmer?
The stopping distance of an automobile is 100 m.
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A river descends 15 mthrough rapids. The speed of the water is 3.2 m/supon entering the rapids and 13 m/supon leaving. What percentage of the gravitational potential energy of the water鈥揈arth system is transferred to kinetic energy during the descent? (Hint: Consider the descent of, say, 10 kgof water.)
In Fig.8.51, a block slides down an incline. As it moves from point Ato point B, which are 5.0 m apart, force acts on the block, with magnitude 2.0 N and directed down the incline. The magnitude of the frictional force acting on the block is 10 N . If the kinetic energy of the block increases by 35 J between Aand B, how much work is done on the block by the gravitational force as the block moves from Ato B?
A machine pulls a 40 kgtrunk 2.0 mup aramp at a constant velocity, with the machine鈥檚 force on the trunk directed parallel to the ramp. The coefficient of kinetic friction between the trunk and the ramp is 0.40. What are (a) the work done on the trunk by the machine鈥檚 force and (b) the increase in thermal energy of the trunk and the ramp?
Figure 8-20 shows one direct path and four indirect paths from point i to point f. Along the direct path and three of the indirect paths, only a conservative forceacts on a certain object. Along the fourth indirect path, bothand a nonconservative forceact on the object. The change in the object鈥檚 mechanical energy (in joules) in going from i to f is indicated along each straight-line segment of the indirect paths. What is(a) from i to f along the direct path and (b) due to along the one path where it acts?
A 1500 kgcar starts from rest on a horizontal road and gains a speed of 72 km/hin 30 s. (a) What is its kinetic energy at the end of the 30 s? (b) What is the average power required of the car during the 30 sinterval? (c) What is the instantaneous power at the end of the 30 sinterval, assuming that the acceleration is constant?
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