2003 asked in 科學及數學其他 - 科學 · 1 decade ago

calculation-heat

A man is drilling an iron block of 2.5 kg.The power of drill is 2500W.Suppose 60% of the power has been lost as heat and increases the temp. of the iron block.The S.H.C of iron is 470

(a)Find the temp. rise of block in 1 min.

ans:76.6

(b)If water is dripping into the hole at steady rate of 20g s^-1,find the temp. rise of block in 1 min.

ans:14.5

(c)Find the maximum temp. increase of the block if water is dripping into the hole at rate stated in (b).

ans:17.9

Update:

Only help me to do part (c)

1 Answer

Rating
  • 天同
    Lv 7
    1 decade ago
    Best Answer

    (c) The heat gain by the dripping water in 1 sec

    = (20/1000)x 4200 x T

    where T is the rise in temperature of the water, and 4200 J/kg-K is the specific heat capacity of water

    Heat generated by the drill = 2500 x 0.6 J/s

    The temperature of the block will become steady when the heat generated is all taken away by the dripping water.

    i.e. 2500x0.6 = (20/1000)x 4200 x T

    solving for T gets T = 17.9 deg.C

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