P 4. Energy Concepts Revamp Flashcards
Define work
(2-way + 2 things)
- Product of force and distance moved in direction of force
- when force is constant
- Scalar quantity
- Measured in Joules (J)
Work done expressed in a formula?
Work done = force x distance
Work done formula expressed in symbols?
J = N x m
Define J
(Work done formula)
Joules
(J)
Define N
(Work done formula)
Newtons
(N)
Define m
(Work done formula)
Metres
(m)
Define energy
(3 things)
- The ability to do work
- Scalar quantity
- Measured in Joules (J)
1J is the….?
(The joule in the work done formula)
(3-way)
- work done when
- a Force of 1N moves its point of application
- 1m in the direction of that Force
1J = ?
1 Nm
1J in base units?
(3 steps)
- F = ma
- = kgms-2
- 1kgm-2s-2
Show an equation is homogeneous?
If the case calls
What are the 2 formulas for work done?
(1 of them is in the data booklet)
- W = Fx
- W = Fxcosθ
Explain work done = energy
(2 things + 2-way)
- Work be done moving an object
- Same with stopping an object
- Energy at start transferred to work done stopping object
- when it comes to rest (at ground level)
What’s the jig with “ground level” with work done = energy?
(2 things)
- Object may still have GPE (Ep)
- if not at ground level
What is the work energy relationship?
- When object slows/speeds up
- work being done on object
How do u find the work done from object slowing/speeding up?
(3-way)
- Difference in the initial,
- and final kinetic energies
- of the object
How do u find the braking force acting on an object?
(2 things)
- Use W = F x D
- Rearrange for F
What does it mean if “total energy is conserved even though there is a loss in kinetic energy”?
(2-way)
- Work done slowing the car
- is transferred to thermal energy
Work = change in Kinetic energy expressed as in symbols?
(It’s in data booklet)
Fx = ½mv2 - ½mu2
What’s Fx = ½mv2 - ½mu2 used for?
Finding the kinetic energy at the end of journey
How do u find the average resistive force?
(5 ways, step by step)
- Use equation to find GPE
- GPE = KE + wd against friction
- Rearrange for wd
- Then W = FD
- Rearrange for F
What is kinetic energy?
(2-way)
- The energy possessed
- by a moving object
What’s the equation to find kinetic energy?
(In data booklet)
Ek = ½mv2
KE equation expressed in words?
Kinetic energy = ½ x mass x speed2
Define Ek?
(KE equation)
Joules
(J)
Define m
(KE equation)
Mass
(kg)
Define v
(KE equation)
Velocity
(ms-1)
What is Gravitational potential energy? (Ep)
(3-way)
- Energy possessed by an object
- due to its position
- or height about the Earth
What’s the equation to find gravitational potential energy?
(In data booklet)
Ep = mgh
GPE equation expressed in words?
Gravitational energy = mass x gravitational field strength x height
Define Ep?
(GPE equation)
Joules
(J)
Define m
(GPE equation)
Mass
(kg)
Define g
(In data booklet)
(GPE equation)
Gravity
(9.81ms-2)
Define h
(GPE equation)
Height
(m)
How to derive GPE?
(4-way)
- Wd = f x d
- f = ma
- Moving thru air ∴ a = g
- Wd = m x g x h
What is elastic potential energy?
(4-way)
- Potential energy stored
- as a result of deformation
- of an elastic object
- aka stretching of a spring
Define an “elastic object”?
(2 things)
- Can become as it was
- return from deformation
How to find EPE of a wire?
EPE = ½Fx
Define F
(EPE equation)
Average force
(N)
Define x
(EPE equation)
Extension
(m)
But what happens if u sub in force against extension gradient in EPE equation?
U get work done needed to stretch a spring
How to find the work done needed to stretch a spring?
Work = ΔPE = ½kx2
Define k
(Wd needed to stretch a spring)
Spring constant
(k…)
Define x
(Wd needed to stretch a spring)
Distance the stretch of the spring is
(m)
When talking about the conservation of energy of an object, what must be considered?
(3 things)
- Changes in kinetic energy
- Changes in gravitational energy
- When to state it’s max or zero energy
A ball is being thrown up, explain point A
(2 things)
- KE decreases, GPE increases
- KE > GPE
A ball is being thrown up, explain point B
(2 things)
- KE decreases, GPE increases
- GPE > KE
A ball is being thrown up, explain point C
(2 things)
- KE = zero
- GPE = max
A ball is being thrown up, explain point D
(2 things)
- GPE decreases, KE increases
- GPE > KE
A ball is being thrown up, explain point E
(2 things)
- GPE decreases, KE increases
- KE > GPE
When ball being thrown up, how come at point C the KE is zero?
(3 things)
- Object at its highest point
- Briefly has zero velocity
- Therefore zero KE
What does the conservation of energy in a system tell us?
Initial energy for a system = final energy for a system
How do u work out energy lost due to friction?
(2 possible methods)
KE = GPE + heat + sound
GPE = KE + heat + sound
How to find force/distance of energy lost due to friction?
(2-way)
- Heat + sound = work done (Wf)
- Wf = Fx
Define power
(3 things)
- The rate of doing Work
- Scalar quantity
- Measured in watts (W) or Js-1
1 Watt = ?
1Js-1
1Js-1 = ?
1W
The equation for power?
(In data booklet)
P = W/t
Define w
(Power equation)
Energy
(J)
Define t
(Power equation)
Seconds
(s)
What’s the “better” power equation?
(Not in data booklet)
P = Fv
Define F
(“better” power equation)
Force
(N)
Define v
(“better” power equation)
Velocity
(ms-1
Show how fv = w/t is homogenous
(4-way)
- fv = w/t
- maD/t = ½mv2/t
- kgms-2ms-1 = kgm2s-2s-1
- kgm2s-3 = kgm2s-3
What’s the FIRST way to find efficiency %?
% Efficiency = (useful energy output/total energy input) x 100%
What’s the SECOND way to find efficiency &?
& Efficiency = (useful power output/total power input) x 100%
What are Sankey diagrams used for?
- Show efficiency
- by which the width of the arrow
- is the % of energy
Define the conservation of energy?
(5-way B|)
- Energy cannot be created or destroyed
- just transferred from one form
- to another
- or transferred from one place
- to another
What is chemical energy?
(2-way + 1 thing)
- Energy stored in mixtures of chemicals
- or in chemical compounds
e.g. All fuels (coal, oil, gas) store chemical energy (potential)
What is electrical energy?
(3-way)
- Energy transferred in electrical circuits
- by the motion of charger carriers
- such as electrons (kinetic)
What is radiant energy?
(2 things)
- Energy carried by all types of electromagnetic waves
- i.e. electromagnetic spectrum n stuff (kinetic)
What is internal energy?
(4-way)
(Very familiar)
- Energy possessed by a body due to
- the random distribution of
- kinetic and potential energies
- of the molecules which make it up
What is thermal/heat energy
Energy due to temperature of an object (kinetic)
What is sound energy?
(2 things)
- Energy produced by vibrating objects
e.g. musical instruments, speakers
Past paper questions shall be there
.