Work Energy and Power Flashcards
What does the principle of conservation of energy state?
Energy can neither be created nor destroyed
What is Energy measured in? Define its unit.
Energy is measured in joules (J). One joule is equal to the energy needed to raise a 1 N
weight through a vertical height of 1 m.
How can energy be transferred?
- Radiation (light)
- Electrically
- Mechanically (Sound)
Whenever energy is transferred, the total amount of energy after the transfer is always equal
to the total amount of energy before the transfer. The total amount of energy is unchanged.
Why is energy needed? What are the different types of stores?
To move objects, change its shape or warm it up.
Objects can possess energy in different types of stores, including:
* gravitational potential stores (the position of objects in a gravitational field)
* kinetic stores (moving objects)
* thermal stores (hot objects)
* elastic stores (objects compressed or stretched)
What is work done? how is it calculated?
Work is done on an object when a force acting on it makes it move. As a result, energy
is transferred to the object
Work done (J) = force (N) x distance moved in the direction of the force (m)
What is one Joule?
the joule (J), equal to the work done when a force of 1 N moves its
point of application by a distance of 1 m in the direction of the force.
What is the relationship between force and displacement?
Imagine a yacht acted on by a wind force F at an angle θ to the direction in which the yacht
moves. The wind force has a component Fcosθ in the direction of motion of the yacht and a
component Fsinθ at right angles to the direction of motion. If the yacht is moved distance s
by the wind, the work done on it, W, is equal to the component of force in the direction of
motion x the distance moved.
What is the relationship of work done on a Force - distance graph?
W = Fs
The area under the graph represents work done.
What is kinetic energy? Its equation?
Kinetic energy is the energy of an object due to its motion. The faster an
object moves, the more kinetic energy it has.
𝑬𝒌 =𝟏/𝟐𝒎𝒗^2
How is Kinetic energy derived?
Consider an object of mass m, initially at rest, acted on by a constant force F for a time t.
Distance travel: 𝑠 = 𝑢+𝑣 𝑡/2=1/2𝑣𝑡 because u=0
Acceleration 𝑎 = (𝑣−𝑢)/𝑡=𝑣/𝑡
Using Newton’s second law, 𝐹 = 𝑚𝑎=m𝑣/𝑡
Therefore, the work done W by force F to move the object through distance s,
𝑊 = 𝐹𝑠 =𝑚𝑣/𝑡×𝑣𝑡/2=1/2𝑚𝑣^2
Because the gain of kinetic energy is due to the work done. then
Kinetic energy, 𝑬𝒌 = 𝟏/𝟐𝒎𝒗^2
What is potential energy? Equation?
Potential energy is the energy of an object due to its position. If an object of mass
m is raised through a vertical height ∆ℎ at a steady speed, the force needed to
raise it is equal and opposite to its weight mg. Therefore,
the work done to raise the object = force x distance moved
∆𝑬𝒑 = 𝒎𝒈∆h
Describe the energy change of an object released above ground gaining speed as it falls due to negligible air resistance.
Its potential energy therefore decreases
and its kinetic energy increases.
After falling through a vertical height ∆𝒉, its kinetic energy is equal to its loss of
potential energy:
𝟏/𝟐𝒎𝒗^2 = 𝒎𝒈∆𝒉
kinetic energy= loss of potential energy from maximum height
𝟏/𝟐𝒎𝒗^𝟐 = 𝒎𝒈(𝒉𝟎−𝒉)
What is the area under a force-distance graph?
Work done
A fairground vehicle of mass m on a downward track
If a fairground vehicle was initially at rest at the top of the track and its speed is v at the
bottom of the track, then what is its i) kinetic energy, ii) loss of potential energy, iii)
words that has been done at the bottom of the track?
- its kinetic energy = 𝟏/𝟐𝒎𝒗^𝟐
- its loss of potential energy = mgh, where h is the vertical distance between the top
and the bottom of the track - the work done to overcome friction and air resistance= mgh -
𝟏/𝟐𝒎𝒗^2
What is power and its equation?
Power is defined as the rate of transfer of energy its equation is enery over time
P = E/t
It can also be calculated as work done over time when energy is transferred using force.
P = W/t
