3 physics MC, Please help very urgent?

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.