3.3 Work, energy and power Flashcards
What is the equation for work?
Work= force applied x distance moved in the direction of the force
W= Fd
What sort of quantity is work?
Scalar because it has magnitude but not direction.
Define work done.
The work done, or energy transferred is the product of the force and the distance moved by the direction of movement.
What is the unit for work?
Joule (J)/ Newton metre (Nm)
When is one joule of work done?
One joule of work is transferred when a force of 1 newton causes an object to move a distance of 1 metre in the direction of the force.
A body has a resultant force acting in a certain direction, causing the body to accelerated. What is the size of the force in the direction perpendicular to the direction of motion?
The force does no work in a direction perpendicular to the direction of motion.
What is the principle of conservation of energy?
The principle of conservation of energy states that the total energy of a closed system remains constant. Energy can neither be created or destroyed, it can only be transferred from one source to another.
What is a closed system?
A closed system is any system in which all the energy transfers are accounted for. Energy or matter cannot enter or leave a closed system.
What does it mean if a light bulb is 3% effcient?
97% of the energy from the light bulb is wasted while only 3% of energy transferred is transferred usefully to light energy.
What is an objects gravitational potential energy?
The energy an object has because of it’s position.
What factors effects gravitational potential energy?
- Vertical high (m)
- Mass (kg)
- Value of gravitational energy (N Kg-1)
What is the relationship between work done and energy transffered?
work done = energy transferred
What is the equation for gravitation potential energy?
E = mgh
What is the equation for kinetic energy?
Ke = 0.5 x m x v2
What is the relationship between kinetic energy and gravitational potential energy?
loss in potential energy = gain in kinetic energy
mgh = ½mv2
This is an example of the principle of conservation of energy.
What will happen to the kinetic energy of an object if all factors are kept the same, but its velocity is doubled?
When you work out kinetic energy, the velocity is squared. This means if the velocity is doubled, the kinetic energy will increase by a factor of 4.
Define power?
Power is defined as the rate of doing work.
It is the rate at which energy is transferred from one form to another.
What is the unit for power?
Watts (W)
What does it mean is a bulb has a rating of 60W?
It means that it transfers 60J of electrical energy to other forms of energy of every second it is turned on.
What is the equation for power in terms of time and energy?
Power= work done/ time taken
What is the equation for power including force?
Power = force x velocity
What is the equation for efficiency?
Efficiency= (useful output energy/ total input energy) x100
Why do we need to work out the efficiency of a devise?
Transfers can never be 100% efficient, energy is always transferred or other forms, which are not useful.
What is a sankey diagram?
Sankey diagrams are usually used to represent to represent power production and energy problems.
What are the forms energy can come in?
- Kinetic
- Gravitational potential
- Thermal
- Elastic potential
- Nuclear
What machines show the transfer of chemical to heat energy?
Oil burner/ matches
What machines show the transfer of electrical to sound energy?
Radio
What machines show the transfer of chemical to sound and light energy?
Battery operated appliance
What machines show the transfer of nuclear to electrical energy?
Nuclear power station
What machines show the transfer of gravitational potential to kinetic energy?
Roller-coaster/ swing/ pendulum
What machines show the transfer of kinetic to electrical energy?
Generator
What machines show the transfer of electrical to kinetic energy?
Electrical motor
When a catapult is used to launch a paper pellet, why does the paper not keep moving forever?
The amount of initial elastic potential energy is finite and is transferred to a finite amount of kinetic energy in the pellet, which will move until the energy transfers into other forms such as sound and heat.
