Work and Energy Flashcards
What is “Work done”?
When a force moves an object and energy is transferred.
How do you calculate Work done?
Work done = Force x distance, Work = Fd
What energy is transferred if a force of 2N moves a distance of 10m?
Work = Fd Work = 2N x 10m = 20J
If Work lifts an object against gravity what energy is gained?
Potential Gravitational Energy
Calculate the change in E^P (gravitational potential energy) when a person lifts 5kgs from the floor to a shelve 2m high.
E^p = mgh Ep = 5 x 10 x 2 = 100J
What is Kinetic Energy?
The energy of a moving object E^K
If an object is lifted higher what energy increases?
Gravitational Potential Energy (E^P)
How does energy move through a system?
Energy is transferred from object to object
What is happening to energy as an object falls?
E^P, Potential Gravitational Energy is transferred to E^K, Kinetic Energy
What energy is formed when the Kinetic energy of a moving car has the brakes applied?
E^K to Heat in the brakes and tires
What energies are formed when the Kinetic energy of a Wind turbine is transferred?
Electrical, heat and sound.
What energy is formed when a Roller coaster wagon is pulled up a ramp?
Gravitational Potential, heat and sound
The amount of kinetic energy of an object relates to which to factors?
Mass (m) and speed (v)
What is the calculation for E^K, Kinetic Energy?
E^K = ½mv^2
What happens to E^K if the speed is doubled?
4 x E^K
What happens to EK if the speed is trebled?
9 x E^K
Calculate the Kinetic energy of a car with a mass of 800kg traveling at a speed of 10ms^-1
E^K = ½mv^2 E^k = ½800 x 102
E^K = 400 x 100 = 40000 J
How much Work is needed to stop a 800kg car traveling at 10m/s and has 40000J of Kinetic energy?
Work = energy transferred = 40000J of heat to the brakes and tires.
An 800kg car is traveling at 10ms^-1 with 40000 J of energy when the brakes are applied. It stops in 8m. What is the average force excerted by the brakes?
Work = Fd Therefore F = Work / d
F = 40000J / 8m = 5000N
When Work is applied against frictional forces which is the main energy transferred?
Heat
Why do we always show the formula when making calculations?
Marks can be gained for the correct formula even if the answer is wrong.
What unit is Force measured in?
Newtons, N
What unit is used to measure distance?
Metres, m
What units is used for Work?
Joules, J
Name the units of this formula E^K = ½mv^2
E^K is Kinetic energy, m is mass, v is velocity or speed
What is the formula to calculate Power?
P = E/t Power = Energy / time
What is Power?
The rate of doing Work or how quickly energy is transferred
A ball has a mass of 0.1kg is dropped from a height of 1.5m. Assuming all the E^P is turned into E^K. How could you calculate the speed a ball would be falling at the moment before it hits the ground?
First calculate E^P = mgh, then because all E^P will be converted to E^K just before it hits the ground use ½mv^2 to calculate v
Energy in battery contains of what form of energy?
Chemical potential
A ringing bell is an example of what form of energy/energies?
Kinetic and sound
Food is contains what form of energy?
Chemical potential
A stretched rubber band contains what form or energy?
Elastic potential
What energy transfers take place while a TV is on?
Electrical to heat, light and sound
What energy transfer takes place in an iron
Electrical to heat
Describe the energy transfers that happen as someone parachutes to earth?
E^P decreases as E^K until terminal velocity is reached.
