Chapter 5 - Work, Energy and Power Flashcards
Define work done
Product of the magnitude of the force and the distance moved by the object in the direction of the force.
Define the joule.
Work done when a force of 1N moves an object 1m in the direction of the force.
Define energy
Capacity for doing work
Is energy scalar or vector?
Scalar
Define Kinetic Energy
Energy due to motion
Define Gravitational potential
Potential energy is equal (in magnitude, but negative) to the work done by the gravitational field moving a body to its given position in space from infinity.
Define Gravitational potential energy
Energy due to it’s height above the ground
Define Elastic potential
the energy stored as a result of a reversible change in an objects shape
Define Electric potential
energy of charges due to their position in a electric field
Define Sound energy
the energy of a mechanical wave due to the movement of atoms
Define internal energy
The sum of randomly distributed kinetic and potential energies of the molecules in a substance
Define electromagnetic energy
the energy from electromagnetic waves, stored within oscillating fields
Define nuclear energy
the energy stored in nuclei released when the nucleons rearrange
Define Chemical energy
the energy contained in chemical bonds, released when atoms rearrange
Principle of conservation of energy
in a closed system, energy cannot be created or destroyed, only transferred from one form to another.
Work done is equivalent to….
energy transfer
Derive equation for KE
- v^2 = u^2 + 2as
- s = v^2/2a
- if work done = force x distance (W = Fx)(x=s)
- W = Fv^2/2a
- F=ma, m=F/a
- W = mv^2/2
= 1/2mv^2
Derive equation for GPE
- GPE is an energy so W = Fx
- under gravity, F = mg
- GPE = mgx
- GPE = mgh
derive equation for impact speed under gravity
- mgh = 1/2mv^2
- 2gh = v^2
- v = root(2gh)
Define power
Rate of energy transfer P=E/t or rate at which work is done
Define the watt
rate of energy transfer of 1 joule per second
Equation to find power to move an object at constant velocity
P = Fv
Equation for efficiency
(Useful energy out / Total energy in) x 100
