Force, Work, and Energy Flashcards

Which statement correctly describes the principle of conservation of energy?

Answer: The total energy in a closed system remains constant

The law of conservation of energy states that energy cannot be created or destroyed, only transformed from one form to another.

A book rests on a table. The table exerts an upward normal force on the book. According to Newton's third law, what is the reaction force?

Answer: The book pushing down on the table

Newton's third law: the book exerts an equal and downward force on the table (action-reaction pair must act on different objects).

At what point in a roller coaster ride does a car have maximum kinetic energy (ignoring friction)?

Answer: At the lowest point of the track

At the lowest point, all gravitational potential energy has converted to kinetic energy, so kinetic energy is at its maximum.

An object falls at constant (terminal) velocity through air. What can be concluded about the forces acting on it?

Answer: Gravity and air resistance are equal and opposite

At terminal velocity, acceleration is zero, meaning the net force is zero — gravity downward equals air resistance upward.

A force is applied to an object at an angle of 60° to the horizontal. If the force is 40 N, what is the horizontal component doing work along the horizontal displacement?

Answer: 20 N

Horizontal component = F cos60° = 40 × 0.5 = 20 N.

Which of the following situations involves negative work being done on an object?

Answer: Brakes slowing down a moving bicycle

Braking force acts opposite to the direction of motion, so the work done by friction on the bicycle is negative.

Which form of energy is stored in the food we eat, fuels, and batteries?

Answer: Chemical energy

Food, fuels, and batteries all store energy in chemical bonds, which is released through chemical reactions.