Work Done & Energy Transfer (OCR GCSE Physics A (Gateway)): Flashcards
Exam code: J249
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Define work done in physics.
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Cards in this collection (27)
Define work done in physics.
Work done is the energy transferred when a force moves an object through a distance in the direction of the force.
True or False?
If a force is applied to an object but the object does not move, work is done on the object.
False.
If a force does not cause movement, no work is done — even if the force is large.
Work is done when a force moves an object over a .......... in the direction of the force.
Work is done when a force moves an object over a distance in the direction of the force.
What is the equation for work done?
The equation for work done is:
W = F × s
where W = work done (J), F = force (N) and s = distance (m).
What is the unit of work done?
The unit of work done is the joule (J), also written as the newton-metre (N m).
True or False?
The amount of energy transferred when work is done is equal to the work done.
True.
Energy transferred (in joules) is always equal to work done (in joules).
Complete the table showing the symbols and units for the work done equation.
Quantity
Symbol
Unit
Work done
Force
Distance
Complete the table showing the symbols and units for the work done equation.
Quantity
Symbol
Unit
Work done
W
joules (J)
Force
F
newtons (N)
Distance
s
metres (m)
explain why a bird flying through the air does work against air resistance
As the bird flies, air resistance (drag) acts against its motion over a distance.
This means energy is transferred from the bird's kinetic store to the thermal store of the surroundings.
What is the energy transfer pathway when work is done by a force?
When work is done by a force, the energy transfer pathway is mechanical — a force acts over a distance to move an object.
Define a system in physics.
A system is an object or group of objects that is being studied — it defines the boundaries of the energy transfer being considered.
True or False?
Energy can be created from nothing when it is transferred between stores.
False.
Energy cannot be created or destroyed — it can only be transferred between stores. This is the conservation of energy.
Match each energy store to an example.
Energy store
Example
Chemical
Kinetic
Gravitational potential
Thermal
Match each energy store to an example.
Energy store
Example
Chemical
a battery or food
Kinetic
a moving car
Gravitational potential
a raised object
Thermal
a hot cup of tea
state the four energy transfer pathways
The four energy transfer pathways are:
Mechanical (a force acts over a distance)
Electrical (flow of charge)
Heating (temperature difference)
Radiation (electromagnetic waves)
Define wasted energy.
Wasted energy is energy that is transferred to an unwanted store, reducing the useful output of a system.
True or False?
In a Sankey diagram, the width of each arrow is proportional to the amount of energy transferred.
True.
In a Sankey diagram, wider arrows represent larger amounts of energy being transferred.
A battery powering a torch transfers energy electrically from the chemical store of the battery to the .......... store of the bulb.
A battery powering a torch transfers energy electrically from the chemical store of the battery to the thermal store of the bulb.
describe how to calculate wasted energy using a Sankey diagram
From a Sankey diagram:
wasted energy = total energy in − useful energy out
The width of the wasted arrow represents the energy that is not transferred to the useful store.
What is the energy transfer pathway when a kettle heats water?
Energy is transferred by heating — the thermal store of the kettle element transfers energy to the thermal store of the water.
Define power.
Power is the rate of energy transfer — it measures how quickly energy is transferred or work is done.
True or False?
A more powerful machine always transfers more energy overall than a less powerful one.
False.
A more powerful machine transfers energy faster, but it does not necessarily transfer more energy in total.
Power is the rate of energy transfer. It can be calculated as: P = .......... ÷ t.
Power is the rate of energy transfer. It can be calculated as: P = E ÷ t.
state the unit of power and explain what it means
The unit of power is the watt (W). One watt equals one joule per second (1 J/s) — the rate at which energy is transferred.
What is 1 kilowatt in watts?
1 kilowatt (1 kW) = 1000 watts (1000 W), or 1000 joules of energy transferred per second.
True or False?
Two cars that reach the same final speed have done the same amount of work, but the faster car has more power.
True.
Both cars do the same work, but the faster car completes it in less time, so it has greater power (P = W/t).
Complete the table for the power equation P = E/t.
Symbol
Quantity
Unit
P
E
t
Complete the table for the power equation P = E/t.
Symbol
Quantity
Unit
P
power
watts (W)
E
energy transferred
joules (J)
t
time
seconds (s)
Calculate the energy transferred by a 2500 W oven used for 50 minutes.
Using P = E/t, rearrange to E = P × t.
Convert time: 50 min × 60 = 3000 s.
E = 2500 × 3000 = 7 500 000 J.
What is a power rating?
A power rating tells you the amount of energy an appliance transfers per unit time — a higher rating means energy is transferred more quickly.
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