Energy

Question 1

What is Kinetic energy ?
Do what has no kinetic energy ?
What calculation do you use for kinetic energy ?
What do each symbol mean ?

Answer 1

Kinetic energy is the energy stored in moving objects.
Stationary objects have no kinetic energy.
For kinetic energy you use 
  E     =  0.5 x m x v(squared ) 
   (K)
M= mass (kg)
E      = Kinetic force (joules)
   (K)
V      = speed (m/s)

Question 2

What is elastic potential energy ? 
HINT: 
What are we doing when we stretch a Spring ?
What is this called ? 
So what happens in conclusion ?

Answer 2

When we stretch a spring , we’re applying a force to change the length of the spring .

Applying force like this is called doing ‘work’.

We’re putting energy in to stretch the spring .The stretched spring is storing this energy and we call this energy elastic potential energy

Question 3

What happens if we apply a force onto a spring ?
What is this called ?
What symbol is the extension given ?

Answer 3

If we apply a force onto a spring it will stretch,and we call this stretch the extension.
The extension is given lower case e.

Question 4

What do you have to do if the measurements are not correct to the equation

Answer 4

You will need to convert it

Question 5

What is gravitational potential energy ?

Why is this ?

Answer 5

Gravitational potential energy is the energy stored in an object due to its position above the earths surface.
This is due to the force of gravity acting on an object .

Question 6

What is the calculation for gravitational potential energy ?

Answer 6

E    = m x g x h 
  (p)
E    =gravitational potential energy
  (p) 
M   = mass (kg) 
G   = gravitational field strength (N/kg) 
H   = height (m)

Question 7

What is specific heat capacity ?

define

Answer 7

The Specific heat capacity of a substance is the amount of energy required to raise the temperature of 1kg of the substance by 1*C .

Question 8

What is thermal energy ?

Answer 8

Thermal energy : The energy stored due to an objects temperature .
Elastic potential energy : the energy stored in a stretched spring .

Question 9

What is the law of conservation of mass ?

Answer 9

Energy can be transferred usefully , stored or dissipated but it cannot be created or destroyed

Question 10

What is a pendulum ?
What do scientists call this ?
Define this ?

Answer 10

A pendulum is a mass attached to a string which is attached to a
fixed point .
Scientists call this a system.
A system is just an object or group of objects.

Question 11

What can the energy not do in this system ?
What do scientists call that ?
If we take a snapshot of the pendulum what can we see ?

Answer 11

No energy can enter or leave this system
Scientists call this a closed system .
If we take a snapshot of this pendulum we can see that energy transfers more easily .

Question 12

What happens at the highest point of the pendulum ?

Answer 12

At the highest point the mass has the maximum store of gravitational potential energy .
As the pendulum swings this transfers to the Kinetic energy store.
The mass has the maximum kinetic energy store at the bottom of the swing .
Since that’s where it’s moving at the fastest speed .

Question 13

What happens as the mass swings back up ?

Answer 13

As the mass swings back up the kinetic energy store transfers to the gravitational potential energy store again.

Question 14

Where does friction occur as the pendulum ?

Answer 14

As the the pendulum swings there is friction in the fixed point .
There is also friction as the pendulum passes through the air particles.
Friction causes energy to be transferred to thermal energy stores

Question 15

Where in the pendulum gets warmer ?
Are these stores useful?
Why is this 👆
What will this eventually cause the pendulum to do ?

Answer 15

The fixed point and the air around the pendulum gradually gets warmer.
These stores of thermal energy are less useful.
The energy has been dissipated (wasted).
This will cause the pendulum to gradually swing with less energy and eventually stop .

Question 16

How do we reduce unwanted energy transfer ?

Give examples of this .

Answer 16

We can reduce unwanted energy transfers by reducing friction .
• use a lubricant (eg: oil) on the
fixed point .
• Remove the air particles from around the
pendulum .

Question 17

What store is all the energy at the start of the jump ?

How does the energy change as the jumper falls?

Answer 17

At the start of the jump,all of the energy in the system is the store of gravitational potential energy .
As the jumper falls, energy is transferred from the gravitational potential energy store to the Kendrick energy store .

Question 18

What happens as the bungee rope just starts to tighten ?

What happens when the rope is fully extended ?

Answer 18

When the bungee rope just starts to tighten,the kinetic energy store is now at its maximum .
When the rope is fully extended, the kinetic energy store is 0 . The jumper is not moving .
At this point the energy has been transferred to the elastic energy store.

Question 19

What happens as the jumper now recoils ?

Answer 19

As the bungee jumper now recoils and energy is transferred from the elastic potential energy store back to the kinetic energy store .

Question 20

What happens during the ascent ?

What happens at the top of the ascent ?

Answer 20

During the ascent, energy transfers from the Kinetic energy store back to the gravitational potential energy store .

Finally at the top of the ascent, all of the energy is now in the gravitational potential energy store .

Question 21

What is important about the jumper during the bungee jump ?what is this due to ?(two reasons)

Answer 21

The jumper never returns back to the original position .
This is because energy is dissipated as thermal energy .

This is due to friction with air particles as the jumper passes through the air .
It’s also due to stretching effects in the bungee rope, which is not fully elastic .

Question 22

When is work done ?
What is mechanical work ?
What is electrical work ?

Answer 22

Work is done whenever energy is transferred from one store to another .

Mechanical work involves using a force to move an object .

Electrical work involves a current transferring energy .

Question 23

How does energy move fro the sledge and the dog?

Answer 23

Chemical energy store in the dog
👇
Kinetic energy store in the moving sledge .
👇
Thermal energy store in the sledge + ground .

Question 24

What is the calculation for work ?

Answer 24

Work done = force x Distance

( J) (N) (m)

Question 25

What store does a car that’s moving have ?
What happens when the driver presses on the breaks ?
What does this create ?
How does energy change at this point ?

Answer 25

A car that’s moving has a kinetic energy store .
So when the driver presses on the brakes.The breaks presses on the wheel of the car .

This creates friction between the break and the wheel . At this point the Kinetic energy store of the car is transferred to the thermal energy store in the brakes .

Question 26

What does this mean about the temperature of the breaks ?
How has energy change therefore ?
What does this mean ?

Answer 26

That means the temperature of the breaks increases and the car slows down and stops.
So we’ve transferred energy from the kinetic energy store of the car to the thermal energy store of the brakes.That means we’ve done Work .

Question 27

Define : power

What is 1 watt an energy transfer of ?

Answer 27

Power is the rate at which energy is transferred or the rate at which work is done .

 1 watt (W) is an energy transfer (or work done) 
Of 1 J per second .

Question 28

Power equations

Answer 28

‘Energy transferred (J)
Power (W)= ___________________
Time (s)

                       Work done (J) Power (W) = \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_    
                             Time (s)

Question 29

Efficiency equations

Answer 29

‘Useful power output
Efficiency = _________________
Total power input

          Useful output energy transfer  Efficiency = \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
             Total input energy transfer

Question 30

In a pan of hot water what was wrong with the method of energy transfer ?
What were we expecting and what happened instead ?

Answer 30

In a pan of hot water the method of energy transfer wasn’t very efficient .

We wanted thermal energy to pass from the hob into the water, however a lot of the thermal energy is wasted .

Question 31

Why was thermal energy wasted ?

Answer 31

This is because the thermal energy was passing into the air around the edges of the hob that are not in contact with the pan.
We’ve also got thermal energy passing into the air at the surface of the water.

Question 31

How can we reduce the wasted energy ?

Answer 31

We can reduce this by using a pan with a wider base and a lid .
Both of these reduce unwanted transfer of thermal energy

Question 32

What is the other problem of using a pan to heat water ?
And how can we overcome this ?
What appliance work like this that we use today ?

Answer 32

The other problem is that a lot of thermal energy is actually being used to heat the base of the pan itself .

We can overcome this by placing the heating element inside the water .
And this is how an electric kettle works .

Question 33

What else is a disadvantage if we use a pan ?

Answer 33

Metal is a good conductor of heat so thermal energy will pass through the sides and the lid of the pan into the air in pan .

Question 34

What else is a advantage if we use a kettle ?

Answer 34

Plastic conducts less well than metal so it’s got a lower thermal conductivity .This means that less thermal energy passes through the walls and the lid and into the air.Therefore this makes the kettle a more efficient way of heating water that using a pan.

Question 35

How do you know wether a building is well insulated or a poorly insulated ?

Answer 35

A poorly insulated building has a lot of thermal energy passing out through the walls and the windows of the building .

But a well insulated building has much less thermal energy passing out of the building .

Question 36

What are two factors of how quickly a building loses thermal energy ?

Answer 36

Thermal conductivity - The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material .

Question 37

What are the layers of modern houses ?

How are the thermal conductivities of house built like this ?

Answer 37

Modern houses are built from two
layers: an external brick wall and an internal breeze block.
Between the walls the is a cavity

The thermal conductivities of houses built like this are fairly high.That means a lot of thermal energy can transfer out of the house.

Question 38

How do builders try to prevent this ?

Answer 38

Builders try to prevent this by packing the cavity with insulating material that has a very low thermal conductivity .

This reduces the overall thermal conductivity of the wall by up to x10. So much less thermal energy passes through the walls and escapes from the house .

Question 39

As well as walls where else can thermal energy escape through ?

Answer 39

As well as the walls thermal energy can also escape through the windows .

Single glazed windows have a high thermal conductivity .

Double glazed windows have low thermal conductivity

Question 40

Where can a lot of thermal energy also escape from ?
How can we reduce this ?
And how does this work ?

Answer 40

A lot of thermal energy can escape through the roof of a house.
So we can reduce this with loft insulation .
This works as it has a low thermal conductivity reducing the rate of which thermal energy passes through .

Question 41

What are the two main ways we can reduce thermal energy transfer from a house ?

Answer 41

Construct the building using materials with a low thermal conductivity.

Build the house using thick walls,as this Also reduces the rate of thermal energy transfer .