AP Physics 1: Algebra-Based Practice Quiz: Conservation of Energy

Correct Answer: A

Based on the provided content, 'Mechanical energy is the sum of a system's kinetic and potential energies.' This is the correct definition.

Correct Answer: B

The content explicitly states, 'A system composed of only a single object can only have kinetic energy.' Potential energy is an energy of interaction and requires at least two objects (e.g., an object and the Earth).

Correct Answer: C

The system is just the ball. The Earth is part of the surroundings and its gravitational force does negative work on the ball as it rises. This work transfers energy out of the system, so the ball's kinetic energy (the system's total energy) decreases. This illustrates how the selection of a system determines whether its energy changes.

Correct Answer: C

The system includes both the ball and the Earth, so gravity is an internal conservative force. With no external work or nonconservative forces, the total mechanical energy is constant. As the ball rises, its speed (and thus kinetic energy) decreases, while its height (and thus gravitational potential energy) increases.

Correct Answer: C

The content states, 'If the work done on a selected system is zero and there are no nonconservative interactions within the system, the total mechanical energy of the system is constant.' While total energy is always conserved (D), *mechanical* energy is only conserved under these specific conditions.

Correct Answer: B

Since the ramp is frictionless and the system includes the Earth, there are no nonconservative forces or net external work. Therefore, mechanical energy is conserved. As the block loses height, its potential energy is converted into kinetic energy, causing it to speed up.

Correct Answer: B

Friction is a nonconservative interaction. According to the principles, if there are nonconservative interactions within the system, the total mechanical energy is not constant. Some mechanical energy is transformed into thermal energy, so the sum of kinetic and potential energy decreases. Total energy (including thermal) is still conserved, so C is incorrect.

Correct Answer: D

The statement 'Energy is conserved in all interactions' is a fundamental law of physics. The conservation of *mechanical* energy (C) is a special case that only applies under specific conditions. (A) and (B) are definitions or specific rules, not the overarching principle.

Correct Answer: C

The content states, 'Any change to a type of energy within a system must be balanced by an equivalent change of other types of energies within the system...' In a closed system (no energy transfer with surroundings), if kinetic energy decreases by 25 J, other forms of energy (like potential or thermal) must increase by a total of 25 J to keep the total energy constant.

Correct Answer: C

The system is only the car. The braking force is external, originating from the surroundings (the road). This external force does negative work on the car, transferring energy out of the system (as thermal energy). This illustrates how the selection of a system and the work done on it determine if the system's energy changes.

Correct Answer: B

Mechanical energy is the sum of kinetic and potential energies. If potential energy increases by 50 J and kinetic energy is constant, the total mechanical energy (KE + PE) has increased by 50 J. Therefore, the total mechanical energy is not constant, which implies that positive work was done on the system from an external source.

Correct Answer: B

This question tests the concept that 'the selection of a system determines whether the energy of that system changes.' If the system is only the satellite, the planet's gravity is an external force doing work. If the system is the satellite-planet pair, gravity is an internal force, and the interaction is described by potential energy, allowing for the conservation of mechanical energy (assuming no other external forces).

Correct Answer: C

This is a direct recall question based on the definition provided: 'Mechanical energy is the sum of a system's kinetic and potential energies.' Option A describes kinetic energy, and option B describes potential energy.

Correct Answer: C

The conditions described (zero external work, no nonconservative forces) mean that the total mechanical energy of the system is constant. According to the principle of conservation of mechanical energy, if potential energy decreases, that energy must be converted into an equivalent amount of kinetic energy.

Correct Answer: B

The system is only the probe. The expanding gas from the rocket thruster is part of the surroundings. This gas exerts a force on the probe and does positive work, transferring energy *into* the probe system and increasing its kinetic energy. Therefore, the energy of the system changes.

Correct Answer: C

This is a challenging question about system definition. The system is *only the bob*. Therefore, both the tension from the string and gravity from the Earth are external forces. As the bob swings down, the tension force is always perpendicular to the direction of motion, so it does no work. However, the gravitational force has a component in the direction of motion, so it does positive work on the bob. This work done by an external force transfers energy into the system, increasing its kinetic energy. Therefore, the energy of the system (the bob) increases.