KVPY Sample Paper KVPY Stream-SX Model Paper-11

  • question_answer
    Water is boiled in a rectangular steel tank of thickness 2 cm by a constant temperature furnance. Due to vaporization water level falls at a steady rate of 1 cm in 9 min. calculate temperature of the furnance. Given, K for steel \[=0.2\,cal{{s}^{-1}}{{m}^{-1}}{}^\circ {{C}^{-1.}}\] 

    A) \[150{}^\circ C\]

    B) \[110{}^\circ C\]

    C) \[130{}^\circ C\]

    D) \[200{}^\circ C\]

    Correct Answer: B

    Solution :

    suppose area of the bottom of the tank =\[A\,c{{m}^{3}}\]
    Volume of water that vaporises in 9 min \[\left( or\,540s \right)\] \[=A\times 1c{{m}^{3}}\]
    Mass of water that vaporises in 540s\[=A\,c{{m}^{3}}\times 1gc{{m}^{-3}}=Ag\]
    \[\therefore Q=mL=A\times 540cal\]
    But \[Q=\frac{KA({{T}_{1}}-{{T}_{2}})}{x}\times t\] Or \[{{T}_{1}}-{{T}_{2}}=\frac{Qx}{KAt}\] \[=\frac{A\times 540\times 2}{0.2\times A\times 540}=10\]
    Total temperature of the furnace i.e., \[{{T}_{1}}={{T}_{2}}+10=100+10=110{}^\circ C\]


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