AP Physics 1 - Unit 3 Review - Work, Energy, and Power - Exam Prep

Translational kinetic energy is the energy of motion, defined by the equation KE = 0.5 * m * v^2, where 'm' is mass and 'v' is speed. Kinetic energy cannot be negative and its measurement depends on the observer's frame of reference.

Work is the mechanical energy transferred into or out of a system. For a constant force, work is calculated as W = F * d * cos(theta), where 'F' is the force, 'd' is the displacement, and 'theta' is the angle between the force and displacement. The area under a force times cosine theta vs. position graph represents work.

The work done by a conservative force (e.g., gravity) is independent of the path, depending only on initial and final configurations. Non-conservative forces (e.g., friction, air resistance) depend on the path, and their work done can dissipate energy from a system.

Gravitational potential energy is stored energy due to an object's position in a gravitational field. In a constant field, PEg = mgh. The general form for two objects is PEg = -G * (m1*m2)/r. Potential energy requires at least two objects and can be negative.

Elastic potential energy is stored in elastic materials, like a spring. Its equation is PEe = 0.5 * k * (delta x)^2, where 'k' is the spring constant and 'delta x' is the displacement from equilibrium. Elastic potential energy cannot be negative.

Mechanical energy is the sum of kinetic, gravitational potential, and elastic potential energies. It remains constant if no net work is done on the system and no work is done by non-conservative forces. The principle states that initial mechanical energy equals final mechanical energy, or the change in mechanical energy is zero.

The Work-Energy Principle states that the net work done on an object or system equals the change in its kinetic energy (W_net = change in KE). This principle is universally applicable regardless of the type of forces involved.

When solving energy problems, it's crucial to identify three things: the initial point/configuration, the final point/configuration, and the location of the horizontal zero line for potential energy (unless only calculating the change in gravitational potential energy in a constant field).

Power is the rate at which energy changes or is transferred. Average power is work divided by time (P_avg = W/delta t). Instantaneous power is P_inst = F * v * cos(theta), where 'F' is force, 'v' is instantaneous velocity, and 'theta' is the angle between them. The unit for power is the watt (Joule/second).