MCAT Work and Energy Flashcards
What is work?
The transfer of energy from object to another.
W = F * d * cos (theta).
- When force and distance in same direction the angle is zero.
- When force and distance is in opposite direction the angle is 180.
- If force and distance are perpendicular to each other the angle is 90.
SI unit is the joule ( 1 J = 1N*m)
How do we find work when given a force v. displacement graph
We break up the area under the graph into shapes and use there formulas for areas. This work because the area under the curve represents the amount of work done.
Potential v. Kinetic energy
potential energy is the stored energy an object has due the gravitational forces acting on it. PE = mgh.
Kinetic energy is the energy an object has in motion. KE = 1/2MV^2.
SI unit is the joule
Work- energy theorem
States that the work done on an object is equal to the change in it’s kinetic energy.
W= 1/2 *m *( Vf^2-Vi^2)
Conservative forces
Forces in which the path taken doesn’t matter only the initial and final positions.
There is no loss of energy only transfering.
ie. gravity, PE, KE
How can potential energy be stored in springs?
When the spring is stretched from it’s equilibrium position ( it’s natural length) it stores PE given by the following formula:
PE = 1/2 KX^2
where K = spring constant
X = displacement
It’s a conservative force.
Law of conservation of energy
The total mechanical energy of an object is equal to the sum of it’s kinetic and potential energies.
The law states that for conservative forces all of the potential energy is converted into the kinetic energy.
KE = PE
Law of conservation of energy in spring systems
When a moving object hits a spring the objects kinetic energy is converted into elastic potential energy.
What is power
Power is the transfer of energy per some time.
P = E/t or W/t ( we can incorporate PE or KE for the numerator).
SI unit is the Watt. 1J = 1 watt.
or can be calculated
P = Fd/t or P = FV
How does simple machines work?
Through a mechanical advantage.
Mechanical advantage = Force output/ Force input.
Immovable pulleys v. Movable pulleys
Immovable pulleys- pulley is attached to an immovable joint like a ceiling or wall. Only changes the direction of the tension force not the tension force itself.
M.A. = mg/mg =1
Movable pulleys- pulley system is attached to load.
M.A.= mg/(mg/2) =2
Define the mechanical advantage of pulley system?
It system composes of only immovable pulleys it’s 1.
If it’s composed of only movable pulleys or a mix of immovable and movable pulleys it’s
2^( number of movable pulleys).
Describe how a lever works?
The application of a small force on one end to a greater force on the other end.
M.A. = Fo/Fi = di/do
For levers describe that change in the mechanical advantage in the following situations:
di > do
di < do
di = do
di > do = M.A. > 1
di < do = M.A. < 1
di = do = M.A. = 1
How does inclined planes function?
Simple machines that allows us to use a force less than the weight of the object to transport it to some height.
The force perpendicular to the gravitational force is the normal force.
The gravitational force can be seperated into parallel and perpendicular vectors.
Parallel = mg sin theta
Perpendicular = mg cos theta
