Kinetic Theory of Temperature and Pressure AP Physics 2 MCQ – Exam Style Questions etc.
Kinetic Theory of Temperature and Pressure AP Physics 2 MCQ
Unit 9: Thermodynamics
Weightage : 15–18%
Exam Style Practice Questions, Kinetic Theory of Temperature and Pressure AP Physics 2 MCQ
Question
The graph above shows the initial and final molecular speed distributions of a gas as a result of a thermodynamic process. Which of the following processes could produce this change?
(A) Expansion of the gas at constant temperature
(B) Compression of the gas with no transfer of energy by heating
(C) Cooling of the gas at constant volume
(D) Cooling of the gas at constant pressure
▶️Answer/Explanation
Ans:B
Question
Two samples of the same type of gas molecules are placed in different closed containers and are thermally isolated from each other and the environment. The figure above shows the distribution of speeds for the molecules in each of the samples. The two samples are now mixed together and allowed to reach thermal equilibrium. Which of the following is true of the peak of the distribution for the mixed sample?
(A) It is closer to 400 m/s than it is to 800 m/s.
(B) It is closer to 800 m/s than it is to 400 m s .
(C) It is midway between the peaks of the distributions shown.
(D) There is not just one peak but two, at the same locations as the peaks of the distributions shown.
▶️Answer/Explanation
Ans:A
Question
Which of the following correctly explain why the pressure of a gas in a rigid container increases with increasing temperature? Select two answers.
A The average molecular kinetic energy increases with temperature, so the molecules exert a larger average force on the walls of the container when they collide with the walls of the container.
B The average molecular kinetic energy increases with temperature, so the molecules exert a larger average force on each other when they collide with each other.
C The average molecular speed increases with temperature, so the molecules collide with the walls of the container more frequently.
D The average molecular speed increases with temperature, so the molecules collide with each other more frequently.
▶️Answer/Explanation
Ans:A , C
The pressure of a gas is the force it exerts on the walls of the container divided by the area of the walls. If the molecules on average are moving faster because of increased temperature, then they exert a greater force on the container walls.
The pressure of a gas is the force it exerts on the walls of the container divided by the area of the walls. If the molecules on average are moving faster because of increased temperature, then they collide with the walls more frequently, increasing the average force exerted on the walls.
Question
A gas enclosed in a cylinder has a pressure of \(2.0×10^5Pa\). The ends of the cylinder have a diameter of 0.40m and the cylinder has a height of 0.30m
. The magnitude of the force exerted by the gas on the wall at one end of the cylinder is most nearly
A \(7.5×10^3N\)
B \(2.5×10^4N\)
C \(7.5×10^4N\)
D \(1.0×10^5N\)
▶️Answer/Explanation
Ans: B
The force on one end wall is related to the pressure by \(F=PA=P(πr^2)\) . Substituting values gives \(F=(2.0×10^5Pa)(π[0.40m/2]^2)=2.5×104N\).
Question
Compressed air in a vertical cylinder with a piston of radius 0.30m is used to lift a crate. The minimum pressure of the air in the cylinder needed for the piston to lift the crate is 1.61×105N/m2, and the pressure in the room outside the piston is \(1.01×105N/m^2\).
If the mass of the piston is negligible, the weight of the crate is most nearly
A \(1.7×10^4N\)
B \(4.6×10^4N\)
C \(7.4×10^4N\)
D \(2.1×10^5N\)
▶️Answer/Explanation
Ans:A
Pressure and force are related by \(P=F/A\) . The difference in pressure between the gas inside the cylinder and the outside air causes an upward force. The force exerted by the pressure difference is \(F=ΔP⋅A=(1.61×105N/m^2−1.01×105N/m^2)(π)(0.3m)^2=1.7×104N\).