Question

1. if a cup of water is sealed and kept at a constant temperature, then what is true about the motion of the water molecules? a. the molecules keep moving at the same average speed. b. the molecules slow down and eventually stop moving. c. the molecules slow down, but the molecules keep moving. d. the molecules are not moving if the cup is sitting still.

Explanation:

In physics (a subfield of Natural Science), the kinetic theory of matter states that molecules are always in motion (Brownian motion, translational/rotational/vibrational motion). Temperature is related to the average kinetic energy of molecules. If temperature is constant, the average kinetic energy (and thus average speed for molecules of the same mass, like water molecules) remains constant. So sealed water at constant temp has molecules moving at same average speed. Option A is correct. Option B is wrong (molecules don't stop as motion is perpetual at non - absolute zero temps). Option C is wrong (temp constant, so speed doesn't slow). Option D is wrong (molecules always move, regardless of cup's motion).

Answer:

A. The molecules keep moving at the same average speed.