Work, Energy & Power Flashcards
Work Done formula
W = F.x.cosØ
Working out ø
Friction = 180 (opposite to motion)
Applied forces = 0 (usually in the d.o.m)
On a slope moving upwards:
ø = 90 + angle of inclination
On a slope moving downwards:
ø = 90 - angle of inclination
When is Work Done = 0?
- No displacement of the object
- Force acts PERPENDICULARLY to displacement (cos90 = 0)
NB about signs!!!
Work Done can be positive OR negative
- Positive means the energy of the system increases
- Negative means the energy of the system decreases
Conservative Force
A force for which the work done in moving an object between two points is independent of the path taken
Non-Conservative Force
A force for which the work done of an object between two points depends on the path taken
eg. f, F applied or T
Gravitational Potential Energy (Ep)
& Formula
The energy an object has because of its position in the gravitational field relative to a reference point
Ep = mgh
NB - VALUE OF g IS ALWAYS POSITIVE
Kinetic Energy (Ek)
& Formula
The energy that an object possesses as a result of its motion
Ek = 1/2mv^2
Mechanical Energy
& Formula
The sum of an object’s potential & kinetic energies
E(mechanical) = Ep + Ek
The Principle of Conservation of Mechanical Energy
& Formula
The total mechanical energy in an isolated system is conserved
& E(mech)i = E(mech)f
Work-energy Theorem
The net work done on an object is equal to the change in the object’s kinetic energy
Wnet = Ekf- Eki
Non-conservative force formula
Wnc = (Ekf - Eki) + (Epf - Epi
Work Done by Fg (other method)
Wfg = - (Epf - Epi)
Power
The rate at which work is done
Power Formulae
P = W/t
P(ave) = F.v(ave)
