It takes fewer and fewer workers to produce crops in developed countries because of substitution of machines that ultimately run on fossil fuel for hand labor
What will be an ideal response?
That is the case—the use of mechanical aids has replaced human labor. According
to the book, Figure 24.9, there is a ratio of 10 to 1 of energy output to input. Richard
Manning in Harper's Magazine from February 2004 wrote, in concurrence, "A two-pound
bag of breakfast cereal burns the energy of a half-gallon of gasoline in its making. All
together the food-processing industry in the United States uses about ten calories of fossil
fuel energy for every calorie of food energy it produces."
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The total force on an object is zero. The angular momentum of the object
A) is zero. B) may be changing. C) can only be changing direction. D) is constant. E) can only be changing magnitude.
A straight wire carries a current of 40 A in a uniform magnetic field (magnitude = 80 mT). If the force per unit length on this wire is 2.0 N/m, determine the angle between the wire and the magnetic field
a. either 39° or 141° b. either 25° or 155° c. either 70° or 110° d. either 42° or 138° e. either 65° or 115°
Carnot Engine: An ideal Carnot heat engine operates between reservoirs at 1740 K and 150 K. In each cycle, 260 J of heat energy is rejected to the low temperature reservoir. In each cycle, how much mechanical work W is performed by the engine?
Fill in the blank(s) with the appropriate word(s).
If you stand in front of a concave mirror, exactly at its focal point,
A) you won't see your image because there is none. B) you will see your image, and you will appear smaller. C) you will see your image at your same height. D) you will see your image and you will appear larger. E) you won't see your image because it's focused at a different distance.