In which of the following states would one mole of water molecules have the most
ID: 961728 • Letter: I
Question
In which of the following states would one mole of water molecules have the most kinetic energy?
a. Liquid water, 70C b. Liquid water, 100C c. Water vapor, 100C d. Water vapor, 70C
In which of the following states would one mole of water molecules have the least kinetic energy?
a. Liquid water, 70C b. Liquid water, 100C c. Water vapor, 100C d. Water vapor, 70C
A juggler throws a sword up in the air. Choose the best statement about the energy of the sword.
a. The kinetic energy of the sword remains constant while it is flying upward. b. The kinetic energy of the sword increases until it reaches a maximum at the highest point.
c. The potential energy of the sword remains constant while it is flying upward. d. The potential energy of the sword increases until it reaches a maximum at the highest point.
A car accelerates from 30 mph to 55 mph while ascending a ramp onto a highway. Which source of potential energy contributes most to the kinetic energy required to ascend the ramp?
a. The gravitational potential energy of the driver’s foot before pressing the gas pedal. b. The gravitational potential energy of the entire car before ascending the ramp.
c. The chemical potential energy of the fuel and/or battery pack. d. The chemical potential energy of the exhaust as it leaves the tailpipe.
Please Show any work
Explanation / Answer
Solution.
Kinetic energy is directly proportional to the temperature. Vapor always has greater kinetic energy than the liquid at the same temperature, because of the greater distance between molecules.
Therefore,
1) Water vapor at 100 °C has the most kinetic energy;
2) Liquid water at 70 °C has the least kinetic energy;
In macro-world, the potential energy is directly proportional to the altitude, Ep = mgh, and the kinetic energy is proportional to the square of the speed Ek = mv2/2.
Therefore,
3) The potential energy of the sword increases until it reaches a maximum at the highest point.
4) The car transforms chemical energy of fuel into kinetic energy of a movement. Therefore, the chemical potential energy of the fuel and/or battery pack contributes most to the kinetic energy required to ascend the ramp.