not assessed paper 2

Question 1

what does it mean if an object has been elastically deformed?

Answer 1

it can go back to its original shape and length after the force has been removed

Question 2

what are objects that can be elastically deformed called?

Answer 2

elastic objects

Question 3

what does it mean if an object has been inelastically deformed?

Answer 3

it doesn’t return to its original shape and length after the force has been removed

Question 4

what happens when a force stretches or compresses an object?

Answer 4

work is done - energy is transferred to the elastic potential energy store of the object

Question 5

where is energy transferred to if an object is elastically deformed?

Answer 5

the object’s elastic potential energy store

Question 6

what is the relationship between the extension of a spring and the force applied to the spring?

Answer 6

they are directly proportional

Question 7

what is the equation that links the Spring constant, the force applied and the extension/compression? (include units)

Answer 7

Force (N) = spring constant (N/m) x extension/compression (m)
F = ke

Question 8

what does the spring constant depend on?

Answer 8

the material that you are stretching - a stiffer spring has a greater spring constant

Question 9

will the extension of a spring carry on increasing proportionally to the force applied forever?

Answer 9

no

Question 10

what is the limit of proportionality?

Answer 10

the point where extension stops being proportional to force - the spring has stretched too far. On an extension-force graph, the graph starts to curve after the limit of proportionality

Question 11

describe a practical to investigate the link between force and extension

Answer 11

1. set up a clamp stand so that a spring is hanging next to a fixed ruler
2. measure the natural length of the spring (when no load is applied) with a millimetre ruler clamped to the stand. Make sure you take the reading at eye level and add a marker (e.g. a thin strip of tape) to the bottom of the spring to make the reading more accurate
3. at a mass to the spring and allow it to come to rest. Record the mass and measure the new length of the spring. The extension is the change in length
4. remove the mass and check that the spring returns to the same length as before (that the limit of proportionality hasn’t been reached)
5. repeat this process, adding more mass each time, until you have at least 6 measurements
6. plot a force-extension graph of your results. It will only start to curve if you exceed the limit of proportionality.

Question 12

what is the gradient of a force-extension graph (with force on the y-axis)?

Answer 12

the spring constant

Question 13

what formula should be used to find the work done in stretching (or compressing) a spring (so long as the spring is not stretched past its limit of proportionality)? (give units)

Answer 13

Elastic potential energy (J) = 1/2 x spring constant (N/m) x extension (m)
Ee = (1/2)ke^2

Question 14

how do you use a force-extension graph to find the energy in the elastic potential energy store of a stretched spring?

Answer 14

you find the area under the line of the graph up to that point

Question 15

what can the formula Ee = (1/2)ke^2 be used for?

Answer 15

1. finding the work done by stretching or compressing a spring
2. calculating the energy stored in a spring’s elastic potential energy store
3. calculating the energy transferred to the spring as it’s deformed (or transferred by the spring as it returns to it’s original shape)

Question 16

what is the equation for stopping distance?

Answer 16

stopping distance = thinking distance + braking distance

Question 17

what is thinking distance?

Answer 17

how far the car travels during the driver’s reaction time (the time between the driver seeing a hazard and applying the brakes)

Question 18

what is the braking distance?

Answer 18

the distance taken to stop under the braking force (once the brakes are applied)

Question 19

what is the typical car braking distance at 30 mph?

Answer 19

14m

Question 20

what is the typical car braking distance at 60 mph?

Answer 20

55m

Question 21

what is the typical car braking distance at 70 mph?

Answer 21

75 m

Question 22

what two things is your thinking distance affected by?

Answer 22

• your speed - the faster you’re going the further you’ll travel during the time you take to react
• your reaction time - the longer your reaction time, the longer your thinking distance

Question 23

what four things is braking distance affected by?

Answer 23

1. your speed - for a given braking force, the faster a vehicle travels, the longer it takes to stop
2. the weather or road surface - if it is wet or icy, or there are leaves of oil on the road, there is less grip (and so less friction) between a vehicles tires and the road, which can cause tyres to skid
3. the condition of your tyres - if the tyres of a vehicle are bald (they don’t have any tread left) then they cannot get rid of water in wet conditions. This leads to them skidding on top of the water
4. how good your brakes are - if brakes are worn or faulty, they won’t be able to apply as much force as well-maintained brakes, which could be dangerous when you need to brake hard

Question 24

why are speed limits really important?

Answer 24

speed affects the stopping distance so much

Question 25

what does braking rely on?

Answer 25

friction between the brakes and the wheels

Question 26

how do brakes work?

Answer 26

when the brake pedal is pushed, this causes brake pads to be pressed onto the wheels. This contact causes friction, which causes work to be done. The work done between the brakes and the wheels transfers energy from the kinetic energy stores of the wheels to the thermal energy stores of the brakes. The brakes increase in temperature

Question 27

why is it harder to stop vehicles that are going faster?

Answer 27

the faster a vehicle is going, the more energy it has in its kinetic energy stores, so the more work needs to be done to stop it. This means that a greater breaking force is needed to make it stop within a certain distance. A larger braking force means a larger deceleration. Very large decelerations can be dangerous because the may cause brakes to overheat, or could cause the vehicle to skid

Question 28

how can you estimate the braking force needed to stop a car?

Answer 28

use the equation v^2 - u^2 = 2as to find the deceleration, and then use the equation F = ma to find the force

Question 29

what is a typical reaction time?

Answer 29

between 0.2 and 0.9 s

Question 30

what can reaction time be affected by?

Answer 30

tiredness, drugs, alcohol, or distractions

Question 31

why can't you measure reaction times with a stopwatch?

Answer 31

because they're so short

Question 32

name two ways of measuring reaction time

Answer 32

1. using a computer-based test (e.g. clicking a mouse when the screen changes colour) 2. using the ruler-drop test

Question 33

what are the 8 steps to the ruler drop test?

Answer 33

1. sit with your arm resting on the edge of a table (this should stop you moving your arm up or down during the test). Get someone else to hold a ruler so it hangs between your thumb and forefinger, lined up with zero. You may need a third person to be at eye level with the ruler to check it's lined up. 2. without giving any warning, the person holding the ruler should drop it. Close your thumb and finger to try to catch the ruler as quickly as possible 3. the measurement on the ruler at the point where it is caught is how far the ruler dropped in the time it takes you to react. the longer the distance, the longer the reaction time 4. you can calculate how long the ruler falls for (the reaction time) because acceleration due to gravity is constant (roughly 9.8 m/s) 5. you can use the equation v^2 - u^2 = 2as to find the final velocity, and then the equation a = Δv/t to find the time, which is the total reaction time 6. make sure you repeat this experiment lots of times, as it is difficult to do it accurately. 7. make sure it's a fair test - use the same ruler for each repeat, and have the same person dropping it 8. you could try to investigate some factors affecting reaction time, e.g. you could introduce distractions by having some music playing or by having someone talk to you while the test takes place

Question 34

what do all magnets produce?

Answer 34

a magnetic field

Question 35

what is a magnetic field?

Answer 35

a region where other magnets or magnetic materials experience a non-contact force

Question 36

how can you show a magnetic field?

Answer 36

by drawing magnetic field lines

Question 37

what are the two poles that all magnets have?

Answer 37

north and south poles

Question 38

in which direction do magnetic field lines always go?

Answer 38

from north to south

Question 39

what do magnetic field lines show?

Answer 39

which way a force would act on a north pole if it was put at that point in the field

Question 40

what do magnetic field lines that are closer together show?

Answer 40

a stronger magnetic field

Question 41

what happens to a magnetic field the further away from a magnet it gets?

Answer 41

it gets weaker

Question 42

where is a magnetic field the strongest? Where are the magnetic forces strongest?

Answer 42

at the poles of a magnet

Question 43

what do compasses show?

Answer 43

the directions of magnetic fields

Question 44

how can you use a compass to build up an image of what a magnetic field looks like?

Answer 44

you can move a compass around a magnet and trace its position on some paper to build up a picture of what the magnetic field looks like

Question 45

what are the two types of magnet?

Answer 45

permanent and induced

Question 46

which type of magnet produces its own magnetic field?

Answer 46

permanent magnets

Question 47

what are induced magnets?

Answer 47

magnetic materials that turn into a magnet when they're put into a magnetic field

Question 48

the force between permanent and induced magnets is always...

Answer 48

attractive

Question 49

what happens when you take an induced magnet out of a magnetic field?

Answer 49

they quickly lose their magnetism (or most of it) and stop producing a magnetic field