Work and Energy Flashcards
system’s ability to do work
energy
kinetic energy (K)
K = 1/2 mv^2
unit: J = kg*m^2/s^2
gravitational potential energy (U)
U = mgh
unit: J = kg*m^2/s^2
elastic potential energy (U)
U = 1/2 kx^2
unit: J = kg*m^2/s^2
total mechanical energy (E)
E = U + K
path dependent, conserve mechanical energy
e.g. gravitational and electrostatic forces
round-trip path: most equal zero
point-to-point path: must all be equal no matter path taken
conservative forces
conservation of mechanical energy
∆E = ∆U + ∆K = 0 W(conservative) = 0
path dependent, dissipates mechanical energy (as chemical or thermal)
e.g. friction, air resistance, viscous drag
W(nonconservative) = ∆E = ∆U + ∆K, equal to energy lost from system
nonconservative forces
method of energy transfer
work (also heat)
work (W)
W = Fd cos θ
unit: J = kg*m^2/s^2
P-V graph:
work = ?
x-axis = ?
y-axis = ?
work = area under curve x-axis = volume (V) y-axis = pressure (P)
constant volume process, no work
isochoric process
constant pressure process,
W = P∆V
isobaric process
rate at which energy is transferred from one system to another
power
power (P)
P = W/t = ∆E/t
unit: watt (W) = J/s = kg*m^2/s^3
work-energy theorem
W(net) = ∆K = K(f) - K(i)
ratio of magnitudes of force exerted on an object by a simple machine (F(out)) to the force actually applied on the simple machine (F(in))
mechanical advantage
mechanical advantage
mechanical advantage = F(out) / F(in)
pulleys- what is relationship between tension and weight
T(total) = W
where T = tension
and W = mg
efficiency
efficiency = W(out) / W(in) = (load)(load distance) / (effort)(effort distance)
