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Ls 發問於 科學及數學物理學 · 3 年前

3 physics MC, Please help very urgent?


3. B

10. A


Why statement (3) in question 3 is correct? The area under the pv graph from V1 to V2 of gas X and Y is different. The work done should be different so as the change in internal energy.

Why 10 is A? I don't understand the question. The acceleration should be 18 - 6 - 2g sin30. Why the question add the statement : the block is pulled by 3m in 1.6 s?

Why 25 is B not C? shouldn't the true resistance be put in the denominator?

Please explain these 3 q to me thanks

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1 個解答

  • 天同
    Lv 7
    3 年前

    3. The area under the pv graph represents the work-done by the gas. It doesn't not represent the gas internal energy. Internal energy of an ideal gas depends on temperature only. Because the two gases expand under constant temperature, the internal energies do not change.

    Notice that when an ideal gas expands isothermally (i.e. under constant temperature), there is heat flow from the surroundings towards the gas so as to maintain the temperature of the gas to be constant.

    10. Net force acting on the mass = (18 - 6 - 2g.sin(30)) N = 2.19 N

    (Take g = 9.81 m/s^2)

    Impulse = force x time = 2.19 x 1.6 Ns = 3.50 Ns

    Because impulse = change in momentum, hence the change in momentum of the mass = 3.50 kg.m/s

    25. Let E be the emf of the cell.

    Actual current (Ia) through the 6-ohm resistor = E/6

    Measured current (Im) using the given ammeter = E/(1 + 6) = E/7

    Error = Ia - Im = E/6 - E/7

    Percentage error = (Ia - Im)/(Ia) =[(E/6 - E/7)/(E/6)] x 100%

    = (1 - 6/7) x 100% = 14.3%

    Note that you should use the actual current as the denominator in the percentage error calculation, as we want to find how much the measured current deviates from the actual current. The actual current should thus be taken as the reference.

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