Work and Energy (Physics Chapter 2) Flashcards
What are the units for the joule(J)?
The units for the joule are (kg x m2) / s2 .
- Essentially, Joules are the force (newtons) applied over a distance.
- Joules are the units for energy.
What is the equation for gravitational potential energy(U) ?
The equation for gravitational potential energy (U) is:
U = mgh
- m = mass of object
- g = acceleration due to gravity
- h = height above datum
What is the equation for elastic potential energy (U) ?
The equation for elastic potential energy (U) is:
U = (1/2) x (k) x (x)2
- k = spring constant (measure of stiffness of spring)
- x = magnitude of displacement from equilibrium
What is total mechanical energy (E)?
Total mechanical energy is another way of expressing the first law of thermodynamics: energy cannot be created nor destroyed.
E = U + K
- U = gravitational potential energy
- K = kinetic energy
What is the equation for determining nonconservative forces?
Wnonconservative = delta (E) = delta (U) + delta (K)
- Nonconservative forces equal the amount of energy “lost” (really transformed into another form of energy) from the system.
What is power and what is its equation?
Power is the rate at which energy is transferred from one system to another. The SI unit for power is the Watt (W) which is equal to joule per second (J/s).
P = (W) / (t) = delta (E) / (t)
- W = work
- delta (E) = the change in total mechanical energy
What is the work-energy theorem and what is its equation?
The work-energy theorem states that the net work done by forces acting on an object will result in an equal change in the ojects’s kinetic energy.
Wnet = delta (K) = Kf - Ki
What is Mechanical Advantage?
Mechanical work is the ratio of force output over force input.
Mechanical Work = Fout / Fin
What is efficiency and what does it measure?
Efficiency compares the work out to work input.
Efficiency = Wout / Win =
(load) (load distance) / (effort) (effort distance)
