H209 First Law of Thermodynamics 2.0 Tutorial (1718)

1 Topic 9: First Law of Thermodynamics Page 1 9749 H2 Physics Tutorial First Law of Thermodynamics Multiple Choice Questions 1. A fixed mass of gas undergoes changes of pressure and volume as shown in Fig. 1. When the gas is taken from state P to state R by the stages PQ and QR, 8J of heat are absorbed by it and 3J of work are done by it. When the same resultant change is achieved by stages PS and SR, 1J of work is done by the gas. In this case, A 12 J of heat are rejected. B 10 J of heat are absorbed. C 8 J of heat are absorbed. D 6 J of heat are absorbed. E 4 J of heat are rejected. (D) J83/II/29; N79/II/31 2. A sample of an ideal gas initially having internal energy U1 is allowed to expand adiabatically performing external work W. Heat Q is then supplied to it, keeping the volume constant as its new value, until the pressure rises to its original value. The internal energy is then U2. (See Fig. 2) The increase in internal energy U2 – U1 is equal to A zero B W C Q D Q - W E W - Q (D) N81/II/27 Fig.1 Fig.2

2 Topic 9: First Law of Thermodynamics Page 2 9749 H2 Physics Tutorial 3. A fixed mass of an ideal gas slowly absorbs 1000 J of heat and as a result expands slowly, at a constant pressure of 2.0 x 104 Pa, from a volume of 0.050m3 to a volume of 0.075m3. What is the effect on the internal energy of the gas? A It decreases by 1000 J. B It decreases by 500 J. C It is unchanged. D It increases by 500 J. E It increases by 1000 J. (D) N90/I/24; J86/I/25 4. A mass of an ideal gas of volume V at pressure p undergoes the cycle of changes shown in the graph. At which points is the gas coolest and hottest? coolest hottest A X Y B Y X C Y Z D Z X E Z Y 5. An ideal gas is taken through the three processes (A  B, B  C, and C  A) shown in the drawing. u is the increase in internal energy, Q is the heat supplied to the gas and W is the work done on the gas. Which of following shows the correct missing entries in the above table? A (b) 500 J (a) 0 B (c) 1436 J (e) -1124 J C (d) -4864 J (b) -561 J D (d) 4303 J (e) 1124 J 0 1 5 1 4 p/ 105 Pa V/ 10-10m3 Z Y X

3 Topic 9: First Law of Thermodynamics Page 3 9749 H2 Physics Tutorial Self-Attempt 6. An ideal gas undergoes an expansion in volume from 1.3 x 10-4 m3 to 3.6 x 10-4 m3 at a constant pressure of 1.3 x 105 Pa. During this expansion, 24 J of heat is supplied to the gas. What is the overall change in the internal energy of the gas? [-6 J] 7. A gas in a cylinder expands from a volume of 0.110 m3 to 0.320 m3. Heat flows into the gas just rapidly enough to keep the pressure constant at 1.80 x 10 5 Pa during the expansion. The total heat added is 1.15 x 105 J. (a) Find the work done by the gas.