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Railways NTPC (Technical Ability) Metal Forming, Casting and Cutting Question Bank Metal Casting

  • question_answer
    2000 cc. of air takes \[1{\scriptstyle{}^{1}/{}_{2}}\]  minutes to pass through a standard Specimen of sand (5.08 cm high and 5.08 cm in dia.). The manometer indicates pressure as \[5\,\text{g/c}{{\text{m}}^{\text{2}}}\text{.}\] In this case the permeability number is:

    A) 30                                

    B) 42

    C) 51                                

    D) 67

    Correct Answer: D

    Solution :

    Permeability number, \[P=\frac{Vh}{pAt}\] \[V\text{ }=\text{ }2000\text{ }c.c.,t=1.5\text{ }min,\text{ }h\text{ }=\text{ }5.08\text{ }cm,\] \[d\text{ }=\text{ }5.08\text{ }cm,\]\[p=5\,\text{g/c}{{\text{m}}^{\text{2}}}\] \[P=\frac{2000\times 5.08}{5\times \frac{\pi }{4}{{(5.08)}^{2}}\times 1.5}=66.83=67\]


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