A ball falls with terminal velocity through air. What is correct about the kinetic energy and the total energy of the ball? Kinetic energy A. B. C. constant increases constant increases Total energy decreases decreases constant constant 5 kineticenergy and the total energy of the ball? Total energy Kineticenergy A. constant decreases increases decreases constant C. constant D. increases constant
The Correct Answer and Explanation is:
Correct Answer: C.
- Kinetic Energy: constant
- Total Energy: decreases
Explanation:
When a ball falls through the air and reaches terminal velocity, it means that the net force acting on the ball becomes zero. This happens when the force of gravity pulling the ball downward is exactly balanced by air resistance (drag force) acting upward. At this point, the ball no longer accelerates and continues to fall at a constant speed — this speed is called the terminal velocity.
Kinetic Energy:
Kinetic energy (KE) is given by the formula:KE=12mv2KE = \frac{1}{2}mv^2KE=21mv2
where mmm is the mass of the object and vvv is its velocity.
Once the ball reaches terminal velocity, its speed remains constant, and therefore, its kinetic energy is also constant. Before reaching terminal velocity, the ball’s speed increases, so its kinetic energy increases. However, after reaching terminal velocity, both speed and kinetic energy stop increasing.
Total Energy:
The total mechanical energy of the ball (ignoring internal energy like heat) is the sum of:
- Kinetic energy: due to motion
- Potential energy: due to height
As the ball falls, it loses gravitational potential energy (since it is getting closer to the ground). However, this lost potential energy does not fully convert into kinetic energy. Instead, a significant portion is transformed into thermal energy due to air resistance (friction with air molecules). This thermal energy is not recoverable mechanical energy and is thus considered a loss from the total mechanical energy.
Therefore, the total mechanical energy of the ball decreases over time due to energy being dissipated as heat, even though the kinetic energy remains constant after terminal velocity is reached.
