Physics 103 : Discussion 22
4. A 40.0g projectile is launched by the expansion of hot gas in an arrangement shown in Figure P12.4a. The cross sectional area of the launch tube is 1.0 cm2, and the length that the projectile travels down the launch tube after starting from rest is 32 cm. As the gas expands, the pressure varies as shown in Figure P12.4b. The values for the initial pressure and volume are Pi = 11 x 105 Pa and Vi = 8.0 cm3, and the final values are Pf = 1.0 x 105 Pa and Vf = 40.0 cm3. Friction between the projectile and the launch tube is negligible.
(a) If the projectile is launched into a vacuum, what is the speed of the projectile as it leaves the launch tube?
(b) If instead the projectile is launched into air at a pressure of 1.0 x 105 Pa, what fraction of the work done by the expanding gas in the tube is spent by the projectile pushing air out of the way as it proceeds down the tube?
12. A quantity of a monatomic ideal gas undergoes a process in which both its pressure and volume are doubled as shown in Figure P12.12. What is the energy absorbed by heat into the gas during this process?
16. A gas is taken through the cyclic process described by Figure P12.16. (a) Find the net energy transferred to the system by heat during one complete cycle. (b) If the cycle is reversed—that is, the process follows the path ACBA—what is the net energy transferred by heat per cycle?
21. A 5.0kg block of aluminum is heated from 20°C to 90°C at atmospheric pressure. Find
(a) the work done by the aluminum,
(b) the amount of energy transferred to it by heat, and
(c) the increase in its internal energy.