Force, Work, and Energy Flashcards

A boy carries a heavy load horizontally across a room at constant height. How much work does gravity do on the load?

Answer: Zero work

Gravity acts vertically downward while displacement is horizontal, so the angle between them is 90°, giving zero work (W = Fd cosθ = Fd cos90° = 0).

Which energy transformation occurs when a stretched rubber band is released and flies across the room?

Answer: Elastic potential → kinetic

The elastic potential energy stored in the stretched rubber band converts to kinetic energy as it moves.

Friction between two surfaces always acts in which direction relative to motion?

Answer: Opposite to the direction of motion

Friction is a resistive force that always opposes the direction of motion or intended motion.

A pendulum swings from its highest point to the lowest point. What happens to its energy?

Answer: Potential energy decreases; kinetic energy increases

As the pendulum falls to its lowest point, gravitational potential energy converts to kinetic energy (ignoring air resistance).

A force of 50 N acts on an object but the object does not move. How much work is done?

Answer: 0 J

Work requires displacement; if the object does not move (d = 0), then W = F × 0 = 0 J.

Which of the following best describes what happens to kinetic energy when an object's speed doubles?

Answer: Kinetic energy quadruples

Since KE = ½mv², doubling v means v² becomes 4v², so kinetic energy quadruples.

The weight of an object on the Moon is less than on Earth because the Moon has:

Answer: A weaker gravitational field strength

Weight = mg; the Moon's gravitational field strength (≈1.6 m/s²) is about one-sixth of Earth's (10 m/s²), so objects weigh less there.