Section 4 - Forces and Energy

Question 1

What is a system?

Answer 1

A single or group of objects

Question 2

What happenes when a system changes?

Answer 2

Energ is transferred

Question 3

What is a closed system?

Answer 3

A system with no net change in energy

Question 4

How can energy be transferred?

Answer 4

Heat
Force
Electricity

Question 5

Describe the energy transfers that occur when the wind causes a windmall to spin?

Answer 5

The wind does work on the windmill causing it to turn and transferring energy to the kinetic energy store of the windmill

Question 6

What is the work done equation?

Answer 6

E = F x d
Energy = Force x Distance

Question 7

What does 1 J equal?

Answer 7

1 Nm

Question 8

What does a force doing work often result in?

Answer 8

A rise in temperature

Question 9

What is power?

Answer 9

How much work is done per second (rate of energy transfer)

Question 10

What is the equation for power?

Answer 10

P = E / t
Power = Energy / Time

Question 11

If an electric heater has a power of 600W and it is left on for 3 seconds, how much energy is transferred?

Answer 11

P = E / t
E = P x t
E = 600 x 3
E = 1800 J

Question 12

A motor does 4.8 kJ of work in 2 minutes

Find its power output?

Answer 12

4.8 kJ = 4800 J

P = E / t
P = 4800 / 120
P = 40 W

Question 13

A constant force of 20 N pushes an object 20 cm

Calculate the work done

Answer 13

E = F x d
E = 20 x 0.2
E = 4 J

Question 14

An appliance transfers 6000 J of energy in 30 seconds

Calculate its power

Answer 14

P = E / t
P = 6000 / 30
P = 200 W

Question 15

What do interactions between objects cause?

Answer 15

Forces

Question 16

What are interaction pairs?

Answer 16

A pair of forces that are equal but opposite

Question 17

What does a free body force diagram show?

Answer 17

An object and all the forces acting on it

Question 18

What should free body force diagrams include?

Answer 18

Every force acting on the body

Question 19

What shouldn’t free body force diagrams include?

Answer 19

The forces the object exerts on the rest of the world

Question 20

What is the resultant force of an object in equilibrium?

Answer 20

Zero

Question 21

What happens to objects that have no resultant force?

Answer 21

They are either stationary or moving at a steady speed

Question 22

How do you draw a scale drawing

Answer 22

Set a scale
Draw the forces acting on an object from tip to tail (one at a time)
Then draw a line from the start to the end
Measure the length and the angle

Question 23

How do you resolve a component force?

Answer 23

Draw it on a scale grid and measure the horizontal and vertical vectors

Question 24

What must a bearing always be presented as?

Answer 24

A three digit number

Question 25

What is a moment?

Answer 25

The turning effect of a force

Question 26

How do you calculate the moment?

Answer 26

``` M = F x d Moment = Force x Distance ```

Question 27

In terms of moment, why is pushing at any other angle bad?

Answer 27

It means a small distance which means a smaller moment

Question 28

What is the principle of moments/

Answer 28

For an object in equilibrium | The sum of the clockwise moments = The sum of anticlockwise moments

Question 29

What do levers do?

Answer 29

Transfer the turning effect of a force

Question 30

How do levers make it easier to do work?

Answer 30

They increase the distance from the pivot at which a force is applied, therefore the smaller the force to give the same moment

Question 31

What are gears used to do

Answer 31

Transmit the rotational effect of a force from one place to another

Question 32

Describe the moment of a small gear with a force applied to it?

Answer 32

A small moment

Question 33

How do gears increase the moment?

Answer 33

If the next gear is larger, the force is applied further from its pivot, so the moment is larger

Question 34

How does the size of the gear affect its speed?

Answer 34

The larger the gear, the slower it spins

Question 35

How do you work out how the speeds and moments will change between gears ?

Answer 35

By looking at the gear ratios

Question 36

The largest gear has 16 teeth and the medium gear has 8 | What is the ratio?

Answer 36

16 : 8 4 : 2 2 : 1

Question 37

If a larger gear and a smaller gear have a ratio of 2 : 1 what does this mean?

Answer 37

For every rotation of the larger gear the smaller gear has rotated twice

Question 38

A 10N force is applied normal to a door, 85 cm from its hinges Calculate the moment created

Answer 38

85 cm = 0.85 m ``` M = F x d M = 10 x 0.85 M = 8.5 Nm ```

Question 39

What is the unit for moment?

Answer 39

Nm

Question 40

What is the ratio of moments of two gears equal to?

Answer 40

The ratio of the gears radii

Question 41

If a gear has 5N applied to it, what is the force of a second gear that is directly connected it?

Answer 41

5N (the same)

Question 42

Describe how to convert between J and Nm?

Answer 42

Divide by 1 (do nothing)

Question 43

What force causes the repulsion of two like electrical charges?

Answer 43

Electrostatic forces of repulsion

Question 44

A parachuter has a weight of 900 N At one point during his fall, the air resistance acting on him is 500 N In what direction is his resultant force at this point?

Answer 44

Down at 400 N (900 - 500 = 400)

Question 45

If a gear is spinning clockwise, what direction will a second gear directly connected to it spin?

Answer 45

Anti-clockwise (the opposite direction)

Question 46

How can you improve the efficiency of a machine that uses gears?

Answer 46

Lubrication, reduce friction which will reduce energy loss through heat