Work and Energy

Question 1

Potential energy

Answer 1

U= mgh

h is correlated with datum (what is labeled as the ground). If h falls past the datum (I.e. Such as diving in water where water is labeled ground), then the distance starts with 0 and decreases. I.e. You jump off a cliff into the water & go 3 feet. From the water you are -3 feet from ground

Question 2

Elastic potential energy

Answer 2

U=1/2kx^2

K is spring constant and x is magnitude of displacement from equilibrium

Question 3

Mechanical energy

Answer 3

E= U + K

Conservative forces (electrostatic/gravity) Delta E = Delta U + Delta K = 0

Non-conservative forces (air resistance/ frictions) Delta E = Delta U + Delta K

Question 4

Work

Answer 4

Many forms. Measured in Joules

W =Fd cos (theta)

IF there’s no change in volume (isovolumetric/isochoric) there’s no work done

W= P•DeltaV (pressure doesn’t change)

If multiple “blocks (areas)” of change in P & V then (pg 58 in physics review)

A1 = 1/2 Delta V • Delta P
A2 = P• Delta V
W= A1 + A2

Question 5

Power

Answer 5

P= Work/time
P=change in energy/ time

Electric power (P)= IV
I=current, V=electrical potential difference (voltage) 

Measure in watts (kg•m^2)/s^3 which is equal to J/s

Question 6

Mechanical Advantage

Answer 6

F(out)/F(in) (Dimensionless)

Question 7

Efficiency

Answer 7

W(out)/W(in)

Load•load distance/ effort•effort distance

Question 8

Kinetic energy

Answer 8

K= 1/2mv^2

Joules (kg•m^2) / s^2