3.3 Work, energy and power

What is work done?

Energy transferred by a force in Joules

What is Kinetic Energy in SI units?

kgm²s⁻²

What is the formula for energy transferred when force is at the angle θ?

W = Fxcosθ

What is the formula for energy transferred when the object moves in the same direction as the force?

W = Fx

What is x in W = Fx?

The distance moved

What does the area underneath a force-displacement graph represent?

The total work done

Define Kinetic Energy

The energy associated with the motion of the object with mass

Define Gravitational Potential Energy

The energy of an object to its position in a gravitational field

Define Elastic Potential Energy

The energy stored by an object as a result of a reversible change in its shape

State the principle of conservation of energy

In a closed system, energy cannot be created or destroyed, but only transferred from one form to another

What is power?

The rate of energy transfer or work done

What formula is used to calculate efficiency?

useful power output / total power output

What is h equal to when an object is falling (ignore air resistance)?

Loss of gravitational potential energy

How much work is done on an object if the force acting on it is perpendicular to the direction that the object is moving?

None

Define 1 Joule

1N x 1m

Show that P = Fv

P = W / t = Fx / t = Fv

What is the formula for the mass per second hitting a wind turbine?

m / t = ρAv

What equation is used to calculate the change in the gravitational potential energy store of an object?

Eₚ = mgh

How can you increase an objects Eₚ?

Lift the object higher

What does the amount of energy in an objects Eₖ depend on?

Its mass and speed

Give the equation used to calculate an object’s kinetic energy

Eₖ = ½mv²

State the relationship between Eₖ and Eₚ

mgh = ½mv²

Why are energy transfers in the real world never 100% efficient?

Restive forces, such as friction and air resistance, means that some energy is always transferred to the thermal energy stores of an object and its surroundings