What is the relationship between work done and energy transferred ?

Work done is equal to the amount of energy transferred.

True or False? If a force acts in the same direction as an object's motion, the object loses energy.

False. If the force acts in the same direction as the object's motion, the object gains energy . If the force acts in the opposite direction to the motion, the object loses energy.

When a force is applied at an angle to an object's direction of motion, which component of the force is used to calculate the work done?

The component of the force parallel to the direction of motion, found by resolving the force vector.

Define the principle of conservation of energy .

Energy cannot be created or destroyed; it can only be transferred from one energy store to another. The total energy in a closed system remains constant.

Name three energy stores.

Kinetic Gravitational potential Elastic Electrostatic Magnetic Chemical Nuclear Thermal

State the four ways in which energy can be transferred between stores.

Mechanical – a force acts on an object, e.g. pushing or pulling Electrical – a charge moves through a potential difference By heating – energy transferred from a hotter object to a colder one By radiation – energy transferred by electromagnetic radiation

Define energy dissipation .

Dissipation describes energy that is wasted because it is transferred to the surroundings (by heating, light or sound) rather than to a useful energy store.

As an object falls freely under gravity, describe the energy transfer that takes place.

Gravitational potential energy is transferred to kinetic energy.

True or False? The same energy transfer that counts as wasted energy in one system is always wasted in every system.

False. What counts as wasted energy depends on the system. For example, light is a useful output for a television but a wasted output for a heater.

A horizontal mass oscillating on a spring transfers energy from the elastic potential store to the .......... store.

A horizontal mass oscillating on a spring transfers energy from the elastic potential store to the kinetic store.

Define efficiency of a system.

Efficiency is the ratio of the useful energy output from a system to the total energy input , often expressed as a percentage.

What does it mean if a system has low efficiency?

Most of the energy transferred by the system is wasted rather than useful.

True or False? Efficiency describes the amount of energy wasted by a system.

False. Efficiency describes the ratio of useful energy output to total energy input . A low efficiency means most energy is wasted, but efficiency itself measures the useful proportion, not the waste.

To convert an efficiency ratio into a percentage, multiply by ..........

To convert an efficiency ratio into a percentage, multiply by 100 .

What types of calculation do efficiency problems often involve?

Energy or power calculations, since efficiency relates useful output to total input in terms of energy or power.

What does the power rating of a household appliance tell you?

The amount of energy transferred electrically from the mains supply per second .

True or False? A 1000 W appliance transfers 1000 J of energy every minute.

False. A 1000 W appliance transfers 1000 J of energy every second , not every minute.

Power can be defined as the .......... of energy transfer.

Power can be defined as the rate of energy transfer.

A LevelPhysicsCambridge (CIE)Flashcards5. Work, Energy & PowerEnergy Conservation

Energy Conservation (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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FrontWork & Energy
Define work done.

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Cards in this collection (30)

Define work done.
Work done occurs when an object is displaced by an external force applied in the direction of its displacement.
$W = F s$
What is the relationship between work done and energy transferred?
Work done is equal to the amount of energy transferred.
True or False?
If a force acts in the same direction as an object's motion, the object loses energy.
False.
If the force acts in the same direction as the object's motion, the object gains energy. If the force acts in the opposite direction to the motion, the object loses energy.
When a force is applied at an angle to an object's direction of motion, which component of the force is used to calculate the work done?
The component of the force parallel to the direction of motion, found by resolving the force vector.
1 N m = 1 ..........
1 N m = 1 J
Define the principle of conservation of energy.
Energy cannot be created or destroyed; it can only be transferred from one energy store to another. The total energy in a closed system remains constant.
Name three energy stores.
- Kinetic
- Gravitational potential
- Elastic
- Electrostatic
- Magnetic
- Chemical
- Nuclear
- Thermal
State the four ways in which energy can be transferred between stores.
- Mechanical – a force acts on an object, e.g. pushing or pulling
- Electrical – a charge moves through a potential difference
- By heating – energy transferred from a hotter object to a colder one
- By radiation – energy transferred by electromagnetic radiation
Define energy dissipation.
Dissipation describes energy that is wasted because it is transferred to the surroundings (by heating, light or sound) rather than to a useful energy store.
As an object falls freely under gravity, describe the energy transfer that takes place.
Gravitational potential energy is transferred to kinetic energy.
True or False?
The same energy transfer that counts as wasted energy in one system is always wasted in every system.
False.
What counts as wasted energy depends on the system. For example, light is a useful output for a television but a wasted output for a heater.
A horizontal mass oscillating on a spring transfers energy from the elastic potential store to the .......... store.
A horizontal mass oscillating on a spring transfers energy from the elastic potential store to the kinetic store.
Define efficiency of a system.
Efficiency is the ratio of the useful energy output from a system to the total energy input, often expressed as a percentage.
State the equation for efficiency in terms of power.
$e f f i c i e n c y = \frac{useful power output}{total power input}$
What does it mean if a system has low efficiency?
Most of the energy transferred by the system is wasted rather than useful.
True or False?
Efficiency describes the amount of energy wasted by a system.
False.
Efficiency describes the ratio of useful energy output to total energy input. A low efficiency means most energy is wasted, but efficiency itself measures the useful proportion, not the waste.
To convert an efficiency ratio into a percentage, multiply by ..........
To convert an efficiency ratio into a percentage, multiply by 100.
What types of calculation do efficiency problems often involve?
Energy or power calculations, since efficiency relates useful output to total input in terms of energy or power.
Define power.
Power is the rate of energy transfer, or work done per unit time.
$P = \frac{E}{t} = \frac{W}{t}$
State the equation for power in terms of work done and time.
$P = \frac{W}{t}$
What does the power rating of a household appliance tell you?
The amount of energy transferred electrically from the mains supply per second.
True or False?
A 1000 W appliance transfers 1000 J of energy every minute.
False.
A 1000 W appliance transfers 1000 J of energy every second, not every minute.
Power can be defined as the .......... of energy transfer.
Power can be defined as the rate of energy transfer.
How can the work done equation be combined with the power equation to find power when force and displacement are known?
$P = \frac{W}{t} = \frac{F s}{t}$
Define power.
Power is the rate at which work is done.
$P = \frac{W}{t}$
State the equation relating power to force and velocity for a body moving at constant velocity, and define each symbol.
$P = F v$
- P = power in watts (W)
- F = force in newtons (N)
- v = velocity in metres per second (m s^-1)
Under what conditions is the equation $P = F v$ valid?
- The force is constant
- The velocity is constant
- The force acts in the same direction as the velocity
For a constant force moving a body at constant velocity, power is given by the equation ..........
For a constant force moving a body at constant velocity, power is given by the equation $P = F v$
True or False?
When a vehicle moves up an incline at constant speed, the force used in $P = F v$ is the vehicle's full weight.
False.
The force used is the component of the weight acting along the incline, $F = m g \sin θ$ , not the full weight.
When a resistive (drag) force acts on an object moving at constant velocity, what value of F should be used in $P = F v$ to find the power needed?
F must be equal to (or greater than) the resistive force, since the applied force needs to overcome it to maintain constant velocity.

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