Question

The temperature of water at the bottom of a large waterfall is higher than that of the water at the top, because

• A. The falling water absorbs heat from the sun.
• B. The water at the bottom has greater potential energy.
• C. The kinetic energy of the falling water is converted into heat.
• D. Rocks on the bed of the river give out heat.

Hint:

When water falls from a height, its potential energy is converted into kinetic energy and then into heat energy.

Answer 1

The Correct Option is C

This phenomenon is explained by the principle of conservation of energy.
At the top of the waterfall, water possesses gravitational potential energy ($PE = mgh$).
As the water falls, its potential energy is converted into kinetic energy ($KE = \frac{1}{2}mv^2$).
When the water hits the rocks and the pool at the bottom, its macroscopic motion (and thus its kinetic energy) is brought to a stop.
This kinetic energy does not disappear; it is converted into other forms, primarily into thermal energy (heat) due to the impact, friction, and turbulence.
This conversion of kinetic energy into heat slightly increases the temperature of the water at the bottom of the waterfall.
Option (C) correctly describes this energy transformation. Options (A), (B), and (D) are incorrect physical explanations.