Energy Flashcards
(90 cards)
1
Q
Ways energy can be stored
A
Kinetic, chemical, thermal, elastic potential, gravitational potential
2
Q
How is chemical energy stored
A
In fuels or in chemicals
3
Q
How is kinetic energy stored
A
In moving objects
5
Q
How is gravitational potential energy stored
A
In objects high up in a gravitational field
6
Q
How is elastic potential energy stored
A
In stretched objects
7
Q
How is thermal energy stored
A
In objects that are hot
9
Q
Ways energy can be transferred
A
Heat,light, sound, electrical
10
Q
Energy transfer diagram for falling object hitting the ground
A
Gravitational potential store -kinetic energy store-Energy transferred to the surroundings - sound and heat
11
Q
Energy transfer diagram for a torch
A
Chemical energy stored in the battery- electrical energy in the wires- Energy transferred to the surroundings- light and heat
12
Q
A stone has dropped from a height explain why all the gravitational potential energy is not transferred into kinetic energy
A
Air resistance, particles rub against, heat energy
13
Q
How does gravitational potential energy and kinetic energy change for a falling object
A
The gravitational potential energy decreases with time while the kinetic energy increases with time
14
Q
The law of conservation of energy
A
Energy cannot be created or destroyed just transferred from one store to the other
15
Q
What is meant by useful and wasted energy
A
Useful energy is transferred to a store that is desired wasted energy cannot be used usefully
16
Q
The useful and wasted energy of a lightbulb
A
Light energy is useful heat energy is wasted
17
Q
Bungee jump energy transfer
A
Gravitational potential energy to kinetic energy
18
Q
Pendulum energy transfer
A
Gravitational potential energy to kinetic energy to gravitational potential energy
19
Q
Useful and wasted energy transfers for a rollercoaster
A
Gravitational potential energy is transferred usefully as kinetic and wastefully as sound and heat
20
Q
Where does wasted energy go
A
Transferred to the surroundings
21
Q
Why does the bungee jump never bounce as high as it started
A
Some of the gravitational potential energy is transferred into heat energy through friction and air resistance
22
Q
Why is the second hill on a rollercoaster never as high as the first
A
Some GPEE energy transferred as heat and sound through friction and air resistance
23
Q
How do brake pads slow down a car
A
The force causes friction and the kinetic energy disperses into heat to the surroundings
24
Q
When the car slows down what energy store changes
A
Kinetic to heat
25
Q
What causes this energy transfer of kinetic to heat energy
A
Friction causes the wheel to heat up
26
Q
What is a closed system
A
An isolated system where no energy transfers take place
27
Unit of energy
Joules
28
Equation for work done
Work done= force x distance
Distance = work done / force
Force= work done / distance
29
The boy pushes a box a distance of 6 m across flat ground with the force of 50N , how much work is done by the boy
Work done =force x distance
| 50N x 6.0m = 300j
30
how would you use a newton metre and a meter ruler to measure the work done by a force
Attach a newton metre to an object
Move the object a measured distance using the meter ruler or lift the object a measured height
Calculate the work done by doing the force x the distance moved
31
Why do meteorites burn up
Air Resistance in the atmosphere causes friction
| Heat is transferred from gravitational potential energy to Kinetic energy
32
Why do breaks get hot
Friction between the wheel and the brake pad cause kinetic energy to be transferred as heat
33
How can you make experiment results more valid
Repeat the experiment and calculate the mean
34
A cyclist applies his brakes. 1400J of work is done to reduce the kinetic energy store and stop the bicycle. The brakes apply a force of 200N. What distance does the bicycle take to stop
```
Distance = 1400j / 200N
Distance = 70m
```
35
In an experiment using a Newton meter to calculate the work done why might the results be different
Different surfaces cause different amounts of friction
36
Equation for gravitational potential energy
GPE = weight x change in height
37
A student of weight 450N steps on a box 0.2 m tall, calculate the increase of his gravitational potential energy store
GPE= 450N x 0.2m
| =90J
38
How could you measure a change in your gravitational potential energy store?
How could you measure a change in your gravitational potential energy store?
Measure your mass in kg on a set of bathroom scales. Multiply this by 9.8N’kg to obtain a value for your weight in Newtons.
Measure the height of a box and step on to it. Multiply your weight by the height of the box to calculate GPE.
39
Equation for gravitational potential energy that uses the effect of gravitational field strength
Gravitational potential energy = mass x gravitational field strength x change in height
40
The gravitational field strength on earth is 9.8N per kg, if a 65 kg person climbs a 10m ladder what is the gravitational potential energy
65 x 9.8 x 10= 6370J
41
A ball stores 100J of gravitational potential energy and is dropped from a height of 10m on Earth. What is the mass of the ball?
100/ 9.8 x 10 = 1.02kg
42
A box of mass 50kg stores 250J of gravitational potential energy on Earth. What is the change in the height of the box?
250/ 50 x 9.8 = 0.51m
43
A ball is dropped from leaning leaning tower of Pisa describe the energy stores changes
At the top the ball stores GPE. As it falls GPE is transferred to KE and heat
due to air resistance. At the ground GPE is zero and all KE is transferred as heat and sound to the surroundings
44
What factors affect the amount of kinetic energy stored in an object
The mass and speed of the object
45
What factors affect the amount of elastic potential energy stored in an object
Spring constant oh how stretchy the object is and the extension of the object
46
Describe the changes in energy stores when an arrow is released from a bow
Elastic potential energy stored is transferred to Kinetic energy. Some energy transferred to heat through air resistance to the surrounding
47
Describe the changes and energy stores when an elastic band is released
The elastic potential energy is stored and transferred to Kinetic energy. Some energy transferred to the surroundings as heat because of air resistance
48
Equation for kinetic energy
Kinetic energy = 1/2 x mass x speed^2
49
Equation for elastic potential energy
Elastic potential energy= 1/2 x Spring constant x extension ^2
50
A vehicle of mass 600kg is moving with a speed of 22m/s. Calculate its kinetic energy store.
KE = 1/2 x 600 x 22 ²
| =145200J
51
A spring has a spring constant k of 0.5N/m. It stretches 20cm when a weight is added to it. Calculate how much elastic potential energy is stored in the spring.
EP = 1/2 x 0.5 x 0.2^2
| =0.01J
52
A sailing boat travels at 13.5m/s and stores 13.7kJ of kinetic what mass is the boat?
Mass= √(2x 13700)/13.5
| =45kg
53
A spring stores 1.5J of elastic potential energy. The spring constant is 0.7N/m.What is the spring’s extension?
Extension = √(2 x 1.5)/0.7
| =2m
54
What is useful energy
Energy transferred to a form that it is desired
55
What is wasted energy
Energy transferred that is cannot be used usefully
56
What form is most energy wasted
Heat energy
57
To where is the energy wasted dissipated
The surroundings or atmosphere
58
When an aeroplane takes off the chemical energy stored is transferred into what new stores
Kinetic gravitational potential (useful)heat and sound(wasteful)
59
How can you use a newton metre to measure the friction force acting on an object
Can be used to pull a object across different surfaces, Pull the object at a constant speed and the value recorded would be the friction force.
60
Identify the useful and wasteful energy of a candle
Chemical energy store= transferred to the surroundings= light( useful ) heat (wasted)
61
Identify the useful and wasted energy of a television
Light and sound( useful) heat(wasted)
62
Describe the ways you can change the frictional forces acting on an object in a lab experiment
```
Change the surfaces that rub together such as:
Use a lubricant
Use ball bearings
Use rougher or smoother surfaces
Use ice
```
63
In an experiment, a kilogram mass is placed on a rough surface and pulled along a distance of 1m with a Newton meter.Repeated measurements are taken.How would you know the results were precise?
There would only be a small difference in the value of each repeat
64
Why would more work have to be done to pull the mass over rough surfaces?
Work is done to overcome friction so heat energy would be lost
65
Ways friction can be useful
Brakes on wheels
Grips on shoes
Nails and screws in wood
66
Three ways friction is unwanted
In machine parts that move
Air resistance on aircraft
Ice skates
67
What is meant by energy efficiency
The amount of energy transferred usefully by a system
68
How efficient can a device be
Can never be 100% efficient
69
How to improve the efficiency of a device
Lubricate moving parts to reduce friction, streamline to reduce air resistance, reduce electrical resistance
70
Energy transfer diagram for a kettle
Electrical energy= heat energy in water , sound energy in surroundings
71
Energy transfer diagram for a motor
Electrical energy= kinetic energy in moving parts, heat energy and sound energy to surroundings
72
Energy transfer Diagram for a heater
Electrical energy= heat and light energy in the surroundings
73
Equation for efficiency
Efficiency = useful energy out / total energy input x 100%
74
A light bulb transfers 40J of electrical energy. 4J is transferred as light and 36J as heat. How efficient is the light bulb?
Efficiency = 4/40 x 100%
| Efficiency =10%
75
Why can the efficiency never be greater than 100%
Because you can never get more energy out than you put in.
76
Explain why the efficiency of a machine or a device can never be equal to 100%
Because there will always be lost energy in heat or sound due to friction or air resistance
77
What four things can energy be wasted in devices
Friction, resistance, air resistance, sound
78
A machine is 25% efficient. The total energy supplied to the machine is 5600J. How much energy is transferred usefully?
25%/100 x 5600
| =1400J
79
For the four things that cause energy to be wasted in electrical and mechanical devices, how can the efficiency be improved?
Friction= lubricant
Resistance = low currents and longer thicker wire
Air resistance = streamline by smoothing surfaces
Sound= lubricate or tighten
80
Electrical appliances in a home and their useful energy transfers
```
Kettle- heat,
vacuum-kinetic
,microwave-heat
,toaster-heat
, television-light and sound, radio-sound,washing machine-kinetic and heat, CD player-kinetic and sound.
```
81
Rank a kettle, lamp, radio and microwave in order of power.
Kettle, microwave, radio, lamp
82
How to test the efficiency of a motor
Connect motor to power supply with a voltmeter and ammeter in the circuit
Use the motor to lift a mass a measured height
Measure the time taken
Record the correct and potential difference
Calculate electrical energy supplied using E = v x I x T
Calculate the GPE with EP= m x g x h
Calculate the efficiency with ef= gain in GPE/ electric energy supplied x 100%
83
In the motor experiment why is the kinetic energy to gravitational potential energy transfer not 100% efficient?
Some energy transferred as heat and sound to surroundings through friction
84
If you double the mass would you need double the amount of energy?
Yes, you would need to increase it more than double because of friction
85
Unit of power
Watt (joule per second)
86
Equation for power
Power= energy transferred / time taken
87
Equation for efficiency using power ratings
Efficiency = useful power output/ total power input x100%
88
Equation for wasted power
Power wasted = total power input - useful power output
89
A motor is supplied with 5000W of power. It transfers 8000J in 20s to gravitational potential energy. Calculate how much energy is supplied to the motor and its efficiency.
Energy supplied=5000W x 20s =1000J
| Efficiency =8000/10000 x 100 = 80%
90
Rank these from least to most powerful : 1kW, 10W,1200W,1MW
1MW, 1200W, 1kW, 10W
91
A 12kW electric shower is used 4 times per day for 20 minutes each time. Calculate the energy supplied to it by the electricity in one day.
Energy = 12000 x (4x20x60)= 57600000J = 57.6 MJ
92
A 12kW electric shower is used 4 times per day for 20 minutes each time. Calculate the energy supplied to it by the electricity in one day. 52MJ is used to heat the water how efficient is the shower.
= 52000000/57600000 x 100
| =90.2%
