3.3 Work, energy and power
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27 Terms
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