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Ganzhou Moore mathematics liberal arts
① Taking cmHg as the unit, the initial pressure of mercury column is (P0-h) cmhg; The pressure after compression is P0;

According to Boyle's law, isothermal compression has:

(p0-h)SL 1=p0SL2

L2 = 30cm

After rebalancing, the mercury levels on both sides are equal, and the gas length is shortened by 10cm, so it is necessary to inject10+19+10 = 39cm of mercury.

(2) the gas is compressed, which is the positive work done by the outside world on the gas;

When the temperature of gas is constant, so is the internal energy. According to the formula of the first law of thermodynamics △U=W+Q, gas gives off heat.

Answer: ① another 39cm mercury column needs to be injected; At this time, the length of the gas column at the closed end is 30cm;;

② In the process of injecting mercury, the outside world does positive work on the enclosed air, and the gas will release heat.