Work, Energy, Power Flashcards
State what is meant by work?
If a force displaces a point (object) along direction of force we say that the force has done work.
Define work done?
Work=Force x Distance travelled along force.
Where:
Work=Nm (Joule)
Force=N
Distance=m
Define what is meant by 1 joule?
If a force of one newton displaces a point by 1 meter along the direction of force a work of one joule is done on the point.
How can we calculate the work done by applied force?
Work done by applied force: Applied force x distance travelled along force.
How do we calculate work done by net force?
Work done by net force acting: Net force x distance.
(F-Fr) s
ma s
How do we calculate work done against resistive forces?
Total resistive forces x distance.
Fr x s
(this is also known as work done dissipated as heat).
What energy is work done equivalent to?
Work done=Change in Kinetic energy
Explain how work done by net force is equivalent to kinetic energy?
Work done by net force=(F-Fr) s
=ma s 2as=v^2-U^2 as=v^2-u^2/2
=m (v^2-u^2/2)
=1/2 m (v^2-u^2)
=1/2 mv^2-1/2mu^2
=change in kinetic energy
How do we calculate work done if force acts an angle?
Work done= Component of force x distance travelled.
W=Fcosθ x S
W=FScosθ
What are the different types of energy?
Electrical energy
Chemical energy
Thermal energy
Atomic Energy
Mechanical energy
What are the two types of mechanical energy?
Potential energy
Kinetic Energy
State what is meant by kinetic energy?
Kinetic energy is the energy of a mass due to its motion.
What are the two types of potential energy?
Gravitational potential energy.
Elastic potential energy.
State what is meant by elastic potential energy?
Elastic potential energy is the energy stored in an object due to extension/compression/change of shape.
State what is meant by gravitational potential energy.
Gravitational potential energy is the energy stored in a mass due to its position in a gravitational field.
What is the formula for gravitational potential energy?
ΔEg=mgΔH
where Eg=Gravitational Potential energy
m=mass
g=gravitational field strength
ΔH=Change in height
What is the formula for Elastic potential energy (strain energy)?
Ee=1/2 Fx
But F=kx
Ee= 1/2 kx^2
If x changes from x1 to x2
ΔE=1/2 k (x2^2-x1^2)
What is the formula for kinetic energy?
1/2 mv^2
What is energy?
Ability to do work is called energy.
If it is done then it is work.
If it can be done it is energy.
What are the two types of energy?
Renewable sources and Non Renewable sources of energy.
What are renewable sources of energy?
Sources that are available in abundance and will not run out in the near future.
Give examples of renewable sources of energy.
Solar energy (Wind/Hydroelectric)
Nuclear energy
Geothermal energy
Tidal energy.
What are non-renewable sources of energy?
Energy sources that are scarce and will eventually run out, in the foreseeable future.
Give an example of non-renewable
Fossil fuel.
What is change of energy equal to?
Change of energy=Work done by the system.
What is the law of conservation of energy?
Energy can neither be destroyed nor created, it is always conserved. We can only convert one form to the other.
What is a transducer?
Any object or system that converts one form of energy to another is called a transducer.
Give an example of a transducer.
A dry cell converts chemical energy to electrical energy or for a falling rock gravitational potential energy is converting into kinetic energy.
How do we calculate efficiency?
Efficiency= Useful output/Total Input
Where input and output are measured in power or energy/ W or J
What are the units of efficiency?
Efficiency has no units because it is a ratio between same quantities.
How do we calculate percentage efficiency?
% efficiency=efficiency x 100.
Percentage efficiency= Useful Output/Total input x 100
Define power.
Power=Work Done/Time taken.
P=W/t
Power=Watt
Work Done=Joule
Time taken=seconds
What is one watt.
Watt is a unit of power, if a work of one joule is done, in one second a power of one watt is developed.
How can we calculate work done when given energy?
Work done=Energy converted from one form to the other.
