Topic 8- Forces And Energy

Question 1

What is the principle of the conservation of energy ?

Answer 1

The principle of the conservation of energy says that energy cannot be created or destroyed.
It can only be transformed from one store of energy into another.

Question 2

What are the 4 ways energy can be transformed ?

Answer 2

Waves
Electrical work
Mechanical work
Heating

Question 3

How does an electrical current transfer energy ?

Answer 3

An electrical current transfers energy from one object to another

such as a battery powering a torch

Question 4

How do waves tranfer energy ?

Answer 4

Light and other types of waves can transfer energy from one object to another.

Question 5

How does mechanical work transfer energy ?

Answer 5

Energy transferred from one object to another via a force is an example of mechanical work.

When an object falls from a building, the weight does mechanical work to transfer energy from the gravitational potential store to the kinetic store.

When you push a wheelchair, energy is transferred to the kinetic store of the wheelchair.

Question 6

How does heating transfer energy ?

Answer 6

Heating an object transfers energy to its internal store (the sum of the energy in the kinetic and chemical stores of its particles).

Question 7

Which principle tells us that energy cannot be created or destroyed ?

Answer 7

Conservation of energy

Question 8

What is the work done by a force equal to ?

Answer 8

The work done by a force is equal to the energy transferred to the object.

Question 9

Fact

Answer 9

More work is done if you:
Push with the same force for a longer distance.
Push with a larger force for the same distance.

Question 10

Work done = ?

Answer 10

force x distance (moved along the line of action of the force)

Question 11

What is transferred to an object that has had work done on it?

Answer 11

Energy

Question 12

What quantitie is considered in the equation for work done ?

Answer 12

Force

Question 13

The work done by a force is equal to what ?

Answer 13

The work done by a force is equal to the change in energy of the object (the energy transferred to the object).

Question 14

How is work done measured ?

Answer 14

The work done (measured in joules)

Question 15

What is work done equal to (detail) ?

Answer 15

is equal to the force (in newtons) multiplied by the distance moved in the direction of this force (in metres).

Question 16

A book is pushed 60cm along a desk by applying a force of 12N. What is the work done on the book?

Answer 16

A book is pushed 60cm along a desk by applying a force of 12N. What is the work done on the book?
W = F × d
60 cm = 0.6 m
W = 12 N × 0.6 m
W = 7.2 J

Question 17

Energy = ? x ? x ?

Answer 17

Energy = potential difference x current x time

Question 18

What is the electrical energy transferred to an component when a current of 3A and a potential difference of 2V act on it for 4s?

Answer 18

E = V I t

E = 2 x 3 x 4

E = 24 J

Question 19

Energy = power x ?

Answer 19

Energy = power x time

Question 20

What is power ?

Answer 20

Power is the rate of energy transfer (or work done).

Question 21

What is power equal to ?

Answer 21

The power (measured in watts) is equal to the work done (in joules) divided by the time taken (in seconds).

Question 22

Whats teh equation for power ?

Answer 22

Power = worl done / time

Question 23

When one store of energy is transferred to another, some energy is wasted (transferred into unwanted stores of energy).

What happens ro this ?

Answer 23

This dissipates (spreads out) to anything nearby.

Question 24

In almost every energy transfer, friction creates what energy and what hppens to this energy ?

Answer 24

In almost every energy transfer, friction creates heat energy and this energy is often wasted.

Question 25

Car engines make a lot of noise and get hot when they are being used to move you about.

What is the useful energy store and wasted energy store ?

Answer 25

The useful energy store here is the kinetic store because you want the car to move you from one place to another.

The heat and sound energy are wasted energy because they are of no use to you.

Question 26

When wires are used in an electrical circuit, they heat up this is often not useful energy.
So what can we say about the heat energy ?

Answer 26

and so it is wasted

Question 27

The efficiency of an energy transfer can never be more than what ?

Answer 27

100

Question 28

What is the equation for the efficiency of (energy in joules) ?

Answer 28

Efficiency = (useful energy output/total energy input) x 100.

The useful energy output and total energy input are measured in joules (J).

Question 29

What is the equation for the efficiency of power in watts ?

Answer 29

Efficiency (power in watts)

Efficiency = (useful power output/total power input) x 100.

The useful power output and total power input are measured in watts (W).

Question 30

What diagrams can show energy transfers ?

Answer 30

Sankey diagrams

Question 31

How much energy is wasted by a 10% efficient filament bulb with 5 J of input?

Answer 31

4.5 J

Question 32

Perpetual machines can continue moving forever without ever stopping. Why are perpetual motion machines impossible?

Answer 32

In every process some energy is waisted
This waste of energy means that the efficiency of energy transfer is less than 100%.
This means that the machine would eventually stop

Question 33

How is efficiency most often expressed ?

Answer 33

As a percentage