Work is the amount of energy transferred when an external force causes an object to move over a distance in the direction of the force.

When a force acts at an angle to an object's motion, only the .......... of the force parallel to the displacement does work.

When a force acts at an angle to an object's motion, only the component of the force parallel to the displacement does work.

True or False? A force that acts perpendicular to an object's displacement does work on it.

False. If the force has no component in the direction of motion ( θ = 90°), cos θ = 0, so no work is done.

What happens to an object's energy when a force acts on it in the opposite direction to its motion?

The object loses energy, since work is done against the direction of motion.

Define kinetic energy .

Kinetic energy is the energy an object has due to its motion; it depends on the object's mass and speed.

When a falling object loses gravitational potential energy, what happens to its kinetic energy?

It gains an equal amount of kinetic energy, since the lost gravitational potential energy is transferred into kinetic energy.

In the kinetic energy equation, only the .......... is squared, not the mass or the one half.

In the kinetic energy equation, only the speed is squared, not the mass or the one half.

True or False? A 'loss of kinetic energy' should be given as a negative value.

False. Kinetic energy is a scalar quantity, so a loss in kinetic energy should not include a negative sign.

Define gravitational potential energy .

Gravitational potential energy is the energy stored in a mass due to its position in a gravitational field.

What is the reference point (zero) for gravitational potential energy?

Ground level at the Earth's surface is taken to be zero gravitational potential energy.

If a mass falls, it loses gravitational potential energy, which is converted .......... other forms of energy.

If a mass falls, it loses gravitational potential energy, which is converted to other forms of energy.

True or False? For a falling object, the gravitational potential energy lost at the start equals the kinetic energy gained at the end (ignoring energy losses).

True. This follows from conservation of energy: gravitational potential energy is transferred into kinetic energy as the object falls.

Define the principle of conservation of energy .

The principle of conservation of energy states that energy cannot be created or destroyed, only transferred between forms; the total energy of a closed system remains constant.

Give two common physics examples of energy conservation between gravitational potential energy and kinetic energy.

Any two from: A swinging pendulum An object in free fall Skiing or skydiving , where gravity causes motion and drag is negligible

When conservation of energy calculations are compared with real-life situations, what should be considered?

In reality there are always some energy losses from the system (e.g. to heat or drag), and these should be mentioned when comparing calculated, ideal values to real-life situations.

To apply conservation of energy, .......... are usually ignored during the calculation stage.

To apply conservation of energy, heat losses are usually ignored during the calculation stage.

True or False? The principle of conservation of energy only applies to systems where no energy is transferred to the surroundings.

False. The principle applies to any closed system ; energy can be transferred between forms (e.g. gravitational potential to kinetic), but the total amount remains constant.

Power is the rate at which energy is transferred, or the rate of doing work (work done per unit time).

Power is defined as the work done per unit .......... .

Power is defined as the work done per unit time .

True or False? A lightbulb's power rating only relates to energy transferred by a force doing work.

False. Power simply means energy transferred per unit time, regardless of the type of energy; a lightbulb's power rating relates to electrical energy transferred, not mechanical work.

Which unit prefixes are commonly used with power in physics problems, and what do they represent?

kW = ×10 3 MW = ×10 6 GW = ×10 9

Efficiency is the ratio of the useful power or energy transfer output from a system to its total power or energy transfer input.

What units does efficiency have, and how can it be expressed?

Efficiency has no units , as it is a ratio. It can be expressed as a decimal between 0 and 1, or as a percentage between 0% and 100%.

In a lightbulb, electrical energy is converted to light and heat; the light energy is .......... and the heat energy is wasted.

In a lightbulb, electrical energy is converted to light and heat; the light energy is useful and the heat energy is wasted.

True or False? What counts as 'useful' or 'wasted' energy is fixed and the same for every system.

False. Whether energy is useful or wasted depends on the system; for example, heat is useful in a heater but wasted in a lightbulb.

When solving an efficiency problem, why should you decide where the energy is lost from the system before starting the calculation?

Because the given efficiency applies to a specific stage of the energy transfer. Calculating first and deducting efficiency afterwards can lead to unnecessary work or an incorrect answer.

International A Level (IAL)PhysicsEdexcelFlashcards1. Mechanics & MaterialsWork, Energy & Power

Work, Energy & Power (Edexcel International A Level (IAL) Physics): Flashcards

Exam code: YPH11

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Define work.

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Cards in this collection (36)

Define work.
Work is the amount of energy transferred when an external force causes an object to move over a distance in the direction of the force.
State the equation for work done when a force acts parallel to an object's displacement.
$Δ W = F Δ s$
where F is the force in the direction of motion (N) and s is the displacement (m).
A force acts at an angle θ to an object's displacement. How is the work done calculated?
Only the component of the force parallel to the displacement is used.
If θ is measured from the horizontal: $W = F s \cos θ$
If θ is measured from the vertical: $W = F s \sin θ$
When a force acts at an angle to an object's motion, only the .......... of the force parallel to the displacement does work.
When a force acts at an angle to an object's motion, only the component of the force parallel to the displacement does work.
True or False?
A force that acts perpendicular to an object's displacement does work on it.
False.
If the force has no component in the direction of motion (θ = 90°), cos θ = 0, so no work is done.
What happens to an object's energy when a force acts on it in the opposite direction to its motion?
The object loses energy, since work is done against the direction of motion.
Define kinetic energy.
Kinetic energy is the energy an object has due to its motion; it depends on the object's mass and speed.
State the equation for kinetic energy.
$E_{k} = \frac{1}{2} m v^{2}$
where m is mass (kg) and v is speed (m s^-1).
When a falling object loses gravitational potential energy, what happens to its kinetic energy?
It gains an equal amount of kinetic energy, since the lost gravitational potential energy is transferred into kinetic energy.
In the kinetic energy equation, only the .......... is squared, not the mass or the one half.
In the kinetic energy equation, only the speed is squared, not the mass or the one half.
True or False?
A 'loss of kinetic energy' should be given as a negative value.
False.
Kinetic energy is a scalar quantity, so a loss in kinetic energy should not include a negative sign.
A body's speed increases from 12 m s^-1 to 45 m s^-1. Does its kinetic energy increase by the same factor as its speed?
No. Since $E_{k} \propto v^{2}$ , kinetic energy increases by the square of the factor the speed increases by.
Define gravitational potential energy.
Gravitational potential energy is the energy stored in a mass due to its position in a gravitational field.
State the equation for the change in gravitational potential energy in a uniform gravitational field.
$Δ E_{p} = m g Δ h$
where m is mass (kg), g is the gravitational field strength (m s^-2) and Δh is the change in height (m).
What is the reference point (zero) for gravitational potential energy?
Ground level at the Earth's surface is taken to be zero gravitational potential energy.
Why does the equation $Δ E_{p} = m g Δ h$ only apply near the Earth's surface?
Because it assumes a uniform gravitational field, which is only a valid approximation close to the Earth's surface.
If a mass falls, it loses gravitational potential energy, which is converted .......... other forms of energy.
If a mass falls, it loses gravitational potential energy, which is converted to other forms of energy.
True or False?
For a falling object, the gravitational potential energy lost at the start equals the kinetic energy gained at the end (ignoring energy losses).
True.
This follows from conservation of energy: gravitational potential energy is transferred into kinetic energy as the object falls.
Define the principle of conservation of energy.
The principle of conservation of energy states that energy cannot be created or destroyed, only transferred between forms; the total energy of a closed system remains constant.
Give two common physics examples of energy conservation between gravitational potential energy and kinetic energy.
Any two from:
- A swinging pendulum
- An object in free fall
- Skiing or skydiving, where gravity causes motion and drag is negligible
When conservation of energy calculations are compared with real-life situations, what should be considered?
In reality there are always some energy losses from the system (e.g. to heat or drag), and these should be mentioned when comparing calculated, ideal values to real-life situations.
To apply conservation of energy, .......... are usually ignored during the calculation stage.
To apply conservation of energy, heat losses are usually ignored during the calculation stage.
True or False?
The principle of conservation of energy only applies to systems where no energy is transferred to the surroundings.
False.
The principle applies to any closed system; energy can be transferred between forms (e.g. gravitational potential to kinetic), but the total amount remains constant.
A skier descends a slope, and 15% of the initial gravitational potential energy is not transferred to kinetic energy. How would you set up the energy equation to find the final speed?
Equate 85% of the gravitational potential energy lost to the kinetic energy gained:
$\frac{1}{2} m v^{2} = 0.85 \times m g h$
Define power.
Power is the rate at which energy is transferred, or the rate of doing work (work done per unit time).
State the equation for power.
$P = \frac{W}{t}$
where W is work done (J) and t is time (s).
What is the SI unit of power, and how is it related to joules and seconds?
The watt (W).
$1 W = 1 {J s}^{- 1}$
Power is defined as the work done per unit ...........
Power is defined as the work done per unit time.
True or False?
A lightbulb's power rating only relates to energy transferred by a force doing work.
False.
Power simply means energy transferred per unit time, regardless of the type of energy; a lightbulb's power rating relates to electrical energy transferred, not mechanical work.
Which unit prefixes are commonly used with power in physics problems, and what do they represent?
- kW = ×10³
- MW = ×10⁶
- GW = ×10⁹
Define efficiency.
Efficiency is the ratio of the useful power or energy transfer output from a system to its total power or energy transfer input.
State the equation for efficiency in terms of energy.
$efficiency = \frac{useful energy output}{total energy input}$
What units does efficiency have, and how can it be expressed?
Efficiency has no units, as it is a ratio.
It can be expressed as a decimal between 0 and 1, or as a percentage between 0% and 100%.
In a lightbulb, electrical energy is converted to light and heat; the light energy is .......... and the heat energy is wasted.
In a lightbulb, electrical energy is converted to light and heat; the light energy is useful and the heat energy is wasted.
True or False?
What counts as 'useful' or 'wasted' energy is fixed and the same for every system.
False.
Whether energy is useful or wasted depends on the system; for example, heat is useful in a heater but wasted in a lightbulb.
When solving an efficiency problem, why should you decide where the energy is lost from the system before starting the calculation?
Because the given efficiency applies to a specific stage of the energy transfer.
Calculating first and deducting efficiency afterwards can lead to unnecessary work or an incorrect answer.

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