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Chapter 1: Q20DQ (page 194)
A car speeds up while the engine delivers constant power. Is the acceleration greater at the beginning of this process or at the end? Explain.
The acceleration is greater at the beginning.
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How many times does a typical person blink her eyes in a lifetime?
A shaft is drilled from the surface to the center of the earth (see Fig. 13.25). As in Example 13.10 (Section 13.6), make the unrealistic assumption that the density of the earth is uniform. With this approximation, the gravitational force on an object with mass m, that is inside the earth at a distance r from the center, has magnitude (as shown in Example 13.10) and points toward the center of the earth. (a) Derive an expression for the gravitational potential energyof the object鈥揺arth system as a function of the object鈥檚 distance from the center of the earth. Take the potential energy to be zero when the object is at the center of the earth. (b) If an object is released in the shaft at the earth鈥檚 surface, what speed will it have when it reaches the center of the earth?
How many gallons of gasoline are used in the United States in one day? Assume that there are two cars for every three people, that each car is driven an average of 10,000 miles per year, and that the average car gets 20 miles per gallon.
A driver in Massachusetts was sent to traffic court for speeding. The evidence against the driver was that a policewoman observed the driver鈥檚 car alongside a second car at a certain moment, and the policewoman had already clocked the second car going faster than the speed limit. The driver argued, 鈥淭he second car was passing me. I was not speeding.鈥� The judge ruled against the driver because, in the judge鈥檚 words, 鈥淚f two cars were side by side, both of you were speeding.鈥� If you were a lawyer representing the accused driver, how would you argue this case?
At what distance above the surface of the earth is the acceleration due to the earth鈥檚 gravity 0.980 m/s2 if the acceleration due to gravity at the surface has magnitude 9.8 m/s2?
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