Flashcards Chapter 7

What is the scientific definition of work?

Work is done when a force causes displacement.

What is the formula for kinetic energy?

KE=\frac12mv^2

What does the Work-Energy Theorem state?

The net work done on an object equals its change in kinetic energy: W_{net} = \Delta KE

What is the SI unit of kinetic energy?

Joule (J)

What is the formula for gravitational potential energy?

PE = mgh

What does ΔPE=mgh represent?

The change in potential energy due to a vertical height change.

What is the SI unit of gravitational potential energy?

Joule (J), a derived unit.

Can potential energy be negative?

Yes, depending on the reference point chosen.

What is potential energy relative to?

A chosen zero height (reference level)

What is a conservative force?

A force that does no net work over a closed path.

Give two examples of conservative forces.

Gravity and ideal spring force.

What is the formula for elastic potential energy in a spring?

PE_{spring}=\frac12kx^2{}

What is the spring force equation (Hooke’s Law)?

F= -kx

What does conservation of mechanical energy state (no non-conservative forces)?

KE_0​+PE_0​=KE_f​+PE_f ​

What is a nonconservative force?

A force where energy is lost from mechanical energy (e.g., friction).

What is the general energy equation with nonconservative forces?

KE_0​+PE_0​=KE_f​+PE_f​+W_{nc} ​

What does W_{nc} ​ represent?

Work done by nonconservative forces (often energy lost as heat).

State the law of conservation of energy.

Energy cannot be created or destroyed, only transformed.

Can efficiency be more than 100%?

No, that violates conservation of energy.

What energy types are included in mechanical energy?

Kinetic energy and potential energy.

Is total energy always conserved?

Yes, in a closed system.

What is the formula for power?

P=\frac{E}{t} or P=\frac{W}{t}

What is the SI unit of power?

Watt (W)

What is 1 watt equal to?

1 joule per second

What is an alternative formula for power using force and velocity?

P = Fv

How many watts are in 1 kilowatt?

1000 W

What does higher power mean?

Energy is transferred faster.

What is the power output of a motor that does 3000 J of work in 60 seconds?

P=\frac{3000J}{60s}=50W

What does E represent in P=\frac{E}{t} ​?

Energy supplied or transferred.

What kind of energy transformation happens when an object falls freely?

Gravitational potential energy converts to kinetic energy.

When does a force do no work on an object?

When the force is perpendicular to the object's displacement, because W=Fdcos⁡θ=0W when \theta = 90^\circ

What is the mechanical energy of a system?

The sum of kinetic and potential energy:

E_{\text{mech}} = KE + PE

How is elastic potential energy stored?

In a stretched or compressed spring, proportional to the square of displacement:

PE_{\text{spring}} = \frac{1}{2}kx^2

What does a negative W_{\text{nc}} ​ mean?

Energy was lost from mechanical energy, often as heat or friction.

What determines the reference point for potential energy?

It is chosen arbitrarily, usually where PE is defined to be zero.