Question

question 13 (4 points)
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in which of these scenarios would the law of conservation of energy not apply?
a rock sinks to the bottom of the lake.
an astronaut on the moon tosses a rock upward.
a projectile is launched horizontally in a vacuum chamber.
a small ball is in free fall.

Explanation:

The law of conservation of energy (total energy, including kinetic and potential, is conserved in a closed system with no non - conservative forces like friction from external sources) applies when there are no significant non - conservative forces.

• For an astronaut tossing a rock on the moon: The moon has a gravitational field, and there's negligible air resistance (since the moon has no atmosphere). So, the mechanical energy (kinetic + potential) of the rock is conserved as it moves. The gravitational force is a conservative force here.
• For a projectile launched horizontally in a vacuum chamber: A vacuum means there's no air resistance (a non - conservative force). So, the only force acting on the projectile is gravity (conservative), and mechanical energy is conserved.
• For a small ball in free fall: If we consider the ball - Earth system and ignore air resistance (in ideal free - fall), gravity is the only significant force, and mechanical energy is conserved.
• For a rock sinking to the bottom of a lake: As the rock sinks, it experiences a buoyant force and a significant frictional force (drag) from the water. These are non - conservative forces. The work done by these non - conservative forces means that the mechanical energy of the rock (kinetic + gravitational potential) is not conserved. Some of the mechanical energy is converted into other forms of energy like heat due to friction with the water.

Answer:

A. A rock sinks to the bottom of the lake.