Final answer:
When a cylinder containing gas is heated with the plunger held steady, the kinetic energy and pressure inside the cylinder increase as a result of more forceful molecular collisions.
Step-by-step explanation:
If a cylinder containing gas is heated with the plunger (piston) held steady, the kinetic energy of the gas molecules will increase due to the rise in temperature. According to the kinetic theory of gases, this increase in molecular motion will cause more forceful collisions with the walls of the cylinder, which in turn will lead to an increase in pressure inside the cylinder. If the gas is confined and cannot expand because the plunger is held steady, the pressure continues to rise as long as the temperature increases. This scenario aligns with the principles of the First Law of Thermodynamics, where the internal energy of a system changes due to the work done on it or the heat transfer into or out of the system. In this case, the closed system does work on its surroundings as pressure and temperature rise due to external heating.