Chapter 7 Energy Practice Flashcards

Vocabulary flashcards covering work, power, gravitational potential energy, kinetic energy, conservation principles, and braking distance relationships from Chapter 7 practice questions.

Work (Mechanical)

The product of the force applied to an object and the distance through which that force is applied ($W = F \times d$); for example, pushing a TV set $2\,m$ with an average force of $20\,N$ does $40\,J$ of work.

Work Done by Perpendicular Force

Zero work is done when a force acts at right angles ($90^\circ$) to the direction of motion, such as gravity acting on a bowling ball rolling along a horizontal bowling alley or Nellie carrying a heavy box across a room at constant speed.

Kilowatt-hour

A unit of energy equal to $3.6\text{ million joules}$ ($3.6 \times 10^6\,J$).

Power

The rate at which work is done or energy is transformed ($P = \frac{W}{t}$); for example, performing $100\,J$ of work in $50\,s$ expends $2\,W$ of power.

Work to Elevate a Log

Raising the center of a long uniform log to shoulder level requires twice as much work as raising just one end of the log to shoulder level while the other end rests on the ground.

Gravitational Potential Energy

The stored energy an object possesses due to its elevated location or height relative to a reference level ($PE = mgh$).

Ramp Mechanical Advantage

Rolling an object up a $2\text{-meter-long}$ ramp to reach a vertical elevation of $1\,m$ cuts the required applied force in half compared to lifting it vertically.

Potential Energy of Elevated Mass

The potential energy of a mass relative to the ground calculated as weight times height; for instance, a $2\text{-kg}$ ball held $4\,m$ above the ground has $80\,J$ of potential energy, and Danny Diver weighing $500\,N$ on a $10\text{-m}$ board has $5000\,J$ of potential energy.

Kinetic Energy

The energy possessed by an object due to its motion ($KE = \frac{1}{2}mv^2$); any object with kinetic energy must be moving.

Speed-Kinetic Energy Relationship

Kinetic energy varies with the square of speed ($KE \propto v^2$), so doubling the speed of an object quadruples ($4\text{ times}$) its kinetic energy.

Air Resistance and Kinetic Energy

In the absence of air resistance, a thrown object returns to its initial level with equal kinetic energy ($100\,J$); in the presence of air resistance, it returns with less than its initial kinetic energy.

Mass and Velocity Kinetic Energy Comparison

Because speed is squared in the kinetic energy formula ($KE = \frac{1}{2}mv^2$), a car of half mass traveling at $60\,km/hr$ has greater kinetic energy than a car of full mass traveling at $30\,km/hr$.

Equal Kinetic Energy Speed Dependence

When two objects of different masses have equal kinetic energy moving in the same direction, the object with the smaller mass (such as a Ping-Pong ball compared to a golf ball) must have a greater speed.

Braking Kinetic Energy Transformation

The process where kinetic energy is converted into thermal energy (heat) when brakes are applied to bring a moving vehicle, such as Joshua's bicycle, to a complete stop.

Braking Distance Quadratic Scaling

The skidding distance of a braking vehicle scales with the square of its initial speed ($d \propto v^2$); traveling twice as fast results in four times the skidding distance, while traveling four times as fast results in sixteen times the skidding distance.