Work, Energy, Power Flashcards
Derive the equation Ek = 1/2 mv^2
KE = m x a x distance
KE = (m x s x v^2) /2s
Derive Ep = mgh
When lifting a mass through a height h
Work done = force x height
Force is weight
Weight = mg = mass x 9.81
Work done = mgh
Describe how a data logger is used to determine the average velocity of a card
- Light beam broke when card enters
- Time starts
- Card leaves and light beam reaches other side
- Timer stops
- Timer records the time taken for the care to pass through the light beam
- The data logger needs the length of the card to be inputted
- The data logger calculates the average velocity of the card
- Velocity = width of card/ time taken
Work Done
Work Done = Force x Distance moved in the direction of the force
W = Fx
Units: Nm, J
Gravitational Potential Energy
The capacity for doing work as a result of an object’s position in an uniform gravitational field.
W = Ep = mass x acceleration of free fall x height
Units: J
Kinetic Energy
KE is energy associated with an object as a result of its motion
KE of an object in linear motion is give by:
Ek = (1/2) m v^2
(Since initial velocity is 0)
Units: J
Power
The rate of work done or rate of energy transfer, given by:
P = W/t
Units: Js^-1, W
If there is a constant force, P is given by:
P = Fx/t
Since speed = x/t, therefore P = Force x Speed
Efficiency
The ratio of useful output energy to total input energy, given by:
Efficiency = (useful energy output/ total input energy) x 100%
The greater the efficiency, the greater the percentage of input energy converted
The Principle of the Conservation of Energy
The total energy of a closed system remains constant. Energy can never be created or destroyed, but it can be transferred from one form to another.
What is work done at an angle to motion given by?
W = Fx cosθ
