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PHYSICS, M3 EQ-Bank 9 MC

A sealed metal container holds a fixed mass of gas. The gas is heated, causing its temperature and pressure to increase. Which of the following best explains this change using principles of thermodynamics?

  1. The gas particles gain kinetic energy, move faster, and collide more frequently and forcefully with the container walls, increasing pressure.
  2. The gas expands to occupy a larger volume, so pressure increases as the particles spread out.
  3. Heating the gas creates more gas particles, which increases the pressure inside the container.
  4. The gas becomes more dense as temperature increases, causing the pressure to rise.
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\(A\)

Show Worked Solution
  • When the gas is heated, the thermal energy is transferred to the gas particles, increasing their average kinetic energy.
  • As a result, the particles move faster and collide more frequently and with greater force against the walls of the sealed container.
  • Since pressure is defined as the force per unit area exerted by particles on the container walls, this increase in collision frequency and force leads to a rise in pressure.
  • B is incorrect because it is not as clear an explanation as option A. C is incorrect as the number of gas particles is constant. D is incorrect because gases become less dense as they expand with temperature.

\(\Rightarrow A\)

PHYSICS, M3 EQ-Bank 4 MC

On a cold morning, a sealed football is left outside on the field. Players notice that it feels softer and doesn't bounce as well as it did the day before when it was warmer.

Which statement best explains this observation using thermodynamic principles?

  1. The lower external temperature reduces the internal energy of the air in the ball, decreasing gas pressure and making the ball less elastic.
  2. The cold causes the mass of the gas particles inside the ball to decrease, reducing pressure.
  3. The ball absorbs energy from the cold air, which increases the pressure inside.
  4. The kinetic energy of the gas particles increases in the cold, causing the ball to lose pressure.
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\(A\)

Show Worked Solution
  • The ball feels softer and doesn’t bounce as well because the colder temperature reduces the internal energy of the gas particles inside.
  • A lower temperature means the particles have less average kinetic energy, so they move more slowly and collide with the inner walls of the ball with less force.
  • This results in a decrease in gas pressure, making the ball less firm and less elastic, so it doesn’t rebound as effectively.

\(\Rightarrow A\)

PHYSICS, M3 EQ-Bank 2 MC

Which statement best describes what the temperature of a substance is?

  1. The total energy of all the particles in a substance
  2. The average potential energy of the particles in a substance
  3. The average kinetic energy of the particles in a substance
  4. The amount of heat a substance contains
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\(C\)

Show Worked Solution
  • Temperature is a measure of the average kinetic energy of the particles in a substance.
  • It reflects how fast the particles are moving; higher temperatures correspond to faster-moving particles.
  • It does not measure total energy (which includes both kinetic and potential energies) or the total heat content of the substance.

\(\Rightarrow C\)