P1-P3 Flashcards
What is the equation for kinetic energy?
Give SI units for all quantities involved.
½ m v^2
½ x Mass x (Velocity)²
Energy (J), Mass(kg), Velocity(m/s)
What is the equation for elastic potential
energy? Give SI units for all quantities
involved.
½ k x^2
½ x Spring Constant x (Extension)²
Energy (J), Spring Constant (N/m), Extension(m)
What is the equation for gravity 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), Height (m)
Define the ‘Specific Heat Capacity’ of a
substance.
The amount of energy needed to raise
the temperature of 1 kilogram of a
substance by 1 degree Celsius.
State the units for Specific Heat
Capacity.
J/°C/kg
Joules/Degree Celsius/Kilogram
What is the definition of ‘Power’?
The rate at which energy is transferred
(or rate at which work is done).
State two equations for power. Give SI
units for all quantities involved.
power = energy transferred/time
power = work done/time
Energy (J), Work Done (J), Time (s)
What is the unit of power?
Watt (W)
Two motors lift the same mass through
the same height. Motor A does this in
half the time of Motor B. Which
dissipates the most power?
Motor A.
The energy transferred is the same but
the time taken is less (P=E/t).
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)
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.
Give examples of chemical energy
stores.
● Food
● Fuel (eg. wood, coal, petrol)
● Batteries
State 4 different stores of energy.
- Kinetic Energy
- Gravitational Potential Energy
- Elastic Potential Energy
- Chemical Energy
State the law of energy conservation.
Energy cannot be created or destroyed
(it can only be transferred into different
forms).
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.
What is waste energy?
The energy that is not used by the device
for its desired purpose.
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
State two equations to calculate
efficiency.
=Useful Output Energy Transfer/Total
Input Energy Transfer
=Useful Power Output/Total Power
Output
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)
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.
What key factors affect the rate of
cooling of a building?
● The thickness of the walls
● The thermal conductivity of the walls
State three methods of reducing heat
loss in a building.
- Double glazing
- Loft and wall insulation
- Thicker walls
