Conservative and nonconservative forces Knowledge-Based Practice

Questions

1. 1.

   Which statement correctly describes how nonconservative forces affect the total mechanical energy of a system?

   • A) They can either increase or decrease the mechanical energy depending on whether they do positive or negative work.
   • B) They can only decrease the mechanical energy because their work always converts mechanical energy into thermal energy.
   • C) They cannot change the mechanical energy because total energy is strictly conserved in every physical process.
   • D) They can only change the mechanical energy if conservative forces simultaneously perform an equal amount of opposing work.
2. 2.

   A block slides down an incline where both gravity and kinetic friction act on it. Which statement correctly distinguishes the effect of the conservative gravitational force from that of the nonconservative friction force during this descent?

   • A) Gravity irreversibly converts mechanical energy into thermal energy, whereas friction reversibly stores energy as potential energy.
   • B) Gravity continuously reduces the total mechanical energy of the block-Earth system, whereas friction keeps the mechanical energy constant.
   • C) Both gravity and friction remove mechanical energy from the block and convert it irreversibly into internal thermal energy.
   • D) Gravity reversibly converts potential energy into kinetic energy, whereas friction irreversibly converts mechanical energy into thermal energy.
3. 3.

   How is the work done by a conservative force, $W_{\text{cons}}$, related to the change in a system's potential energy, $\Delta U$?

   • A) $W_{\text{cons}} = -\Delta U$, meaning positive work done by the conservative force decreases potential energy.
   • B) $W_{\text{cons}} = \Delta U$, meaning positive work done by the conservative force increases potential energy.
   • C) $W_{\text{cons}} = \Delta U + \Delta K$, meaning work done by the conservative force equals the total mechanical energy change.
   • D) $W_{\text{cons}} = 0$, meaning a conservative force does no work whenever potential energy changes.
4. 4.

   In an isolated system where an object moves under the influence of a conservative force alone, in which direction does the conservative force act?

   • A) In the direction that increases the total mechanical energy of the system
   • B) In the direction of increasing potential energy of the system
   • C) In the direction of decreasing potential energy of the system
   • D) In a direction perpendicular to the change in potential energy of the system
5. 5.

   When work is done on an object against a conservative force, what happens to the transferred energy within the system?

   • A) It is converted irreversibly into thermal energy and dissipated into the environment.
   • B) It is permanently destroyed, causing a net decrease in the total energy of the universe.
   • C) It continuously increases the total mechanical energy over any completed round-trip path.
   • D) It is stored within the system as potential energy and can be fully recovered as kinetic energy.
6. 6.

   A box slides along a rough horizontal floor in a complete closed loop, returning to its starting point. Which statement correctly describes the total work done on the box by the kinetic friction force during this round trip?

   • A) It is zero because the net displacement of the box is zero.
   • B) It is positive because the work done on the return path offsets the work done on the forward path.
   • C) It is negative because the friction force continuously opposes the motion along the entire path.
   • D) It is zero because the closed path prevents any net transfer of mechanical energy.
7. 7.

   An object moves from position P to position Q along two different trajectories, where Path 1 has a shorter total distance than Path 2. If gravity and kinetic friction both act on the object during the motion, which statement correctly compares the work done by these forces along the two paths?

   • A) Gravity does more work along Path 2, while the magnitude of work done by friction is the same for both paths.
   • B) Both gravity and friction perform identical amounts of work along Path 1 and Path 2.
   • C) Gravity does the same work along both paths, while the magnitude of work done by friction is greater along Path 2.
   • D) Both gravity and friction do zero net work because the initial and final positions are identical for both trajectories.
8. 8.

   A potential energy function can be mathematically defined only for conservative forces. Which of the following forces can be associated with a potential energy function?

   • A) Kinetic friction force
   • B) Elastic force of an ideal spring
   • C) Viscous drag force in a fluid
   • D) Tension force in a moving cable
9. 9.

   An object moves along a path where both conservative and nonconservative forces perform work. Which of the following statements correctly describes the net work done by the nonconservative forces on the system?

   • A) It is always zero because the total energy of an isolated system is strictly conserved.
   • B) It determines the change in the potential energy associated with the system.
   • C) It converts potential energy entirely into kinetic energy without dissipation.
   • D) It is equal to the net change in the total mechanical energy of the system.
10. 10.

    Which of the following characteristics definitively identifies a force acting on an object as conservative rather than nonconservative?

    • A) The total work done by the force on the object along any closed path is zero.
    • B) The magnitude of the work done by the force increases directly with the total path length traveled.
    • C) The force acts perpendicular to the direction of motion at all times during the displacement.
    • D) The force converts mechanical energy directly into thermal energy throughout the motion.

Answers and step-by-step solutions appear after you finish the test.