Energy Transfers Flashcards
What is the equation for gravitational
potential energy? Give SI units for all
quantities involved.
mgh
Mass x Gravitational Field Strength x
Height
Energy (J), Mass(kg), Gravitational Field Strength (N/kg)
What is the equation for kinetic energy? Give SI
units for all quantities involved.
½ m v²
½ x Mass x (Velocity)²
Energy (J), Mass(kg), Velocity(m/s)
What is meant by the conservation of energy?
● The total amount of energy in a closed
system remains constant
● Energy cannot be made or destroyed but
can change from one form to another
Describe the energy changes involved when a ball is
thrown upwards and then returns to its starting
position. Ignore air resistance.
● Upwards: KE is converted to GPE
● Peak: Maximum GPE, zero KE
● Downwards: GPE is converted to KE
KE (Kinetic Energy), GPE (Gravitational Potential Energy)
State any changes in the total energy of a ball that
is kicked, assuming that no external forces act.
The total energy of the system remains
constant due to the conservation of
energy.
Describe the energy changes that occur
in a filament light-bulb.
● Electrical energy is transferred into
light and heat energy
● Light is a useful energy form, heat is
waste energy
Describe the energy transfers for a bungee jumper.
● When falling, the GPE is converted to KE of
jumper
● As the cord tightens, KE is converted and
stored as Elastic Potential Energy (EPE)
● At lowest point, the jumper’s initial GPE
equals the EPE stored in the cord
Explain why a bungee jumper slows down once the
cord begins to stretch.
● Kinetic energy decreases since it is
converted to elastic potential energy
● Since KE is proportional to (velocity)², as KE decreases, so does velocity.
What is waste energy?
The energy that is not used by the device
for its desired purpose, or not converted
into the desired form.
State two equations to calculate efficiency.
=Useful Output Energy / Total Input
Energy
=Useful Power Output/Total Power
Output
State the consequence for energy
transfer of a material with a high thermal
conductivity.
The rate of energy transfer through the
material is higher than for a material with
a lower thermal conductivity.
Do double-glazed windows have a higher or lower
thermal conductivity than single-glazed windows?
Lower, meaning less energy transfers
through them
State three methods of reducing heat
loss in a building
- Double glazing
- Loft and wall insulation
- Thicker walls
How can you reduce unwanted energy
transfer in a mechanical system?
Reduce friction by lubricating moving parts.
How can the efficiency of a system be increased?
1.Reducing waste output (by
lubrication, thermal insulation etc.)
2. Recycling waste output (eg. recycling
thermal waste energy as input energy)
