Chapter 7 Key Ideas
Work is energy transferred to an object.
Energy is the ability to make an object move.
ΣW = ΔK
ΔK = ½mvf2- ½ mvi2
Three ways to approach work/energy problems:
• Sum all forces, find net work
• Find the work associated with each force and sum
• Find the change in kinetic energy, this is equal to the net work
For a constant force: W=Fd cosθ
For gravitational force W=mgh
For a spring force W= ½kxi2- ½ kxf2
General Variable force: F(x)i + F(y)j +F(z)k
For a General Variable Force:
Work = ∫F(x) dx + ∫F(y) dy + ∫F(z) dz from initial to final
values of direction
If no ΔK Net Work = 0
Power: rate of work done on an object per unit time
P = dW/dt (instantaneous power)
P = Δw/Δt (average power)
P=F°v
(instantaneous power or if constant force)