General Physics 1.7 Energy, Work & Power Flashcards
What type of energy is stored in a moving object?
Kinetic energy.
What happens, in terms of energy, when an object is lifted?
Its gravitational potential energy increases.
Give an equation for kinetic energy
kinetic energy (J) = ½ × mass (kg) × velocity^2 (m/s)
E = ½mv^2
Give an equation for gravitational potential energy
Gravitational potential energy (J) = mass (kg) x
height (m) x gravitational field strength (N/kg)
E = mgh
When work is done against friction or resistance, what happens?
There is less of a change in kinetic energy because some energy is dissipated through heating.
What is the original source of most of the energy on Earth?
The sun.
What forms of energy do not ultimately come from the sun?
• Geothermal
• Nuclear
• Tidal
What is the source of the sun’s energy?
Nuclear fusion.
What are the main energy resources available to humans?
Fossil fuels (oil, gas and coal), nuclear fuels, biofuels, wind, hydroelectricity, tides and solar energy.
Define renewable energy.
Energy from a source which does not run out, so can be replenished.
Which energy sources are non-renewable?
• Fossil fuels
• Nuclear fuel
Which energy sources are renewable?
• Biofuels
• Wind
• Hydroelectric and tidal energy
• Geothermal energy
• Solar power
Why is non-renewable energy used to provide electricity on a large scale?
Non-renewable sources tend to have a larger energy output per kilogram of fuel.
What is efficiency?
The ratio of useful work done to energy supplied, often given as a percentage, i.e. the percentage of energy which is converted to a useful form.
Give the equation for efficiency
Efficiency =Useful energy output / Total energy input
You can convert this to a percentage by multiplying the answer by 100.
How can the efficiency of a system be increased?
- Reducing waste output (by lubrication, thermal insulation etc.)
- Recycling waste output (eg. recycling thermal waste energy as input energy)
Define work done.
• Work is done on an object when energy is transferred (from one form to another)
• Equal to the product of force and distance
Give the equation for work done
work done (J) = force (N) × distance (m)
W= Fd
(where distance is the distance moved along the line of action of the force)
Define power.
Power is the rate at which energy is transferred or the rate at which work is done.
Give 2 equations for power
power (W) = energy (J) ÷ time (s)
power (W) = work done (J) ÷ time (s)
