Question

question 1 10 pts choose the incorrect statement. the total kinetic energy plus potential energy of a body can remain constant even if the body’s speed is decreasing. always remains constant if friction is acting. can be negative. always remains constant if the body is in free fall.

Explanation:

Step1: Recall energy - conservation principles

In the presence of non - conservative forces like friction, mechanical energy (sum of kinetic and potential energy) is not conserved. Friction dissipates energy as heat.

Step2: Analyze each option

• Option 1: If speed is decreasing, kinetic energy is decreasing. But if potential energy is increasing by the same amount (e.g., a body moving up a slope), the total mechanical energy can remain constant.
• Option 2: When friction is acting, friction does work against the motion of the body. This work done by friction is dissipated as heat, and the total mechanical energy (kinetic + potential) of the body decreases. So, the statement "always remains constant if friction is acting" is incorrect.
• Option 3: Potential energy can be negative (e.g., gravitational potential energy is negative relative to an arbitrarily chosen zero - level). Kinetic energy is non - negative, but the sum of kinetic and potential energy can be negative if the negative value of potential energy is greater in magnitude than the kinetic energy.
• Option 4: In free - fall, neglecting air resistance (a non - conservative force), only the conservative force of gravity acts. By the law of conservation of mechanical energy, the total mechanical energy (kinetic + potential) remains constant.

Answer:

B. always remains constant if friction is acting.