10 Work, Energy and Power

What is work done equivalent to?

Energy Transferred

What are the SI base units equivalent to the Joule?

kgm²s⁻²

How is work done calculated?

W = F x cosΘ (distance moved x component of the force in the direction of motion)

What is Θ in W = F x cosΘ?

The angle between the force and motion.

What is energy?

The capacity of one object or system to do work (or cause a change) on another.

What is represented by the area under a force-distance graph?

Work done.

What is the principle of conservation of energy?

The energy of a closed system always remains constant. Energy can never be created or destroyed, only transferred.

What form of energy is due to the motion of a mass?

kinetic energy

What form of energy is due to the position of a mass in a gravitational field?

gravitational potential energy

What form of energy is due to the bonds between atoms in a substance?

chemical energy

What form of energy is due to a reversible change in shape of an object?

elastic potential energy

What form of energy is due to the position of a charge in an electric field?

electrical potential energy

What form of energy is due to the forces between protons and neutrons in an atom?

nuclear energy

What form of energy is due to randomly distributed potential and kinetic energies of the atoms within a system?

Thermal energy

What effect does friction have on the energy of a moving object?

Transfers kinetic energy primarily to thermal energy

Describe the energy transformations for an object sliding downhill at constant speed.

Gravitational potential energy decreases at the same rate as work is done by friction.

Describe the energy transformations for a vehicle travelling uphill at constant speed.

Work is being done by the driving force and that is equal to the gain in gravitational potential energy plus work done by friction

What is power?

Power is the rate at which work is done P = W/t

What is the derived unit of Power?

Watt (W)

What are the equivalent SI base units of the Watt?

kgm²s⁻³

What is the equation P = Fv used for?

The power developed by an object moving at constant speed against a constant resistive force.

How is % efficiency calculated?

(Useful output energy/total input energy) x 100