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Test # 54


1.
B is twice fast as A can complete a job in 6 days, how long will it take for both A and B together to complete the same job?

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Idiom of the Day

get up the nerve to (do something)
to become brave enough to do something
I tried to get up the nerve to ask my friend about his new job.
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  • Simple Science

    Man's Strength not Sufficient for Machines

    Man's Way of Helping Himself:
    A machine, an inert mass of metal and wood, cannot of itself do any work, but can only distribute the energy which is brought to it. Fortunately it is not necessary that this energy should be contributed by man alone, because the store of energy possessed by him is very small in comparison with the energy required to run locomotives, automobiles, sawmills, etc. Perhaps the greatest value of machines lies in the fact that they enable man to perform work by the use of energy other than his own.

    Figure shows one way in which a horse's energy can be utilized in lifting heavy loads. Even the fleeting wind has been harnessed by man, and, as in the windmill, made to work for him. One sees dotted over the country windmills large and small, and in Holland, the country of windmills, the landowner who does not possess a windmill is poor indeed.

    For generations running water from rivers, streams, and falls has served man by carrying his logs downstream, by turning the wheels of his mill, etc.; and in our own day running water is used as an indirect source of electric lights for street and house, the energy of the falling water serving to rotate the armature of a dynamo (Section 310).

    A more constant source of energy is that available from the burning of fuel, such as coal and oil. The former is the source of energy in locomotives, the latter in most automobiles.

    In the following Chapter will be given an account of water, wind, and fuel as machine feeders.

    FIG. - Man's strength is not sufficient for heavy work.

    FIG. - The windmill pumps water into the troughs where cattle drink.


    Chourishi Systems