2.3 Forces & Energy

Question 1

Work Done

Answer 1

Force makes an object move, Energy gets transferred - when something beings to move effort is put in
Work done = force x distance - if there is no motion in the direction of the force no work is done by that force

Question 2

Conservation

Answer 2

A energy principle that says energy is always conserved, can’t be created or destroyed but stored or dissipated

Question 3

No Frictional Force

Answer 3

Work done on an object will be equal to the energy transferred usefully - some work must be done against frictional forces causing energy to dissipate - through heating

Question 4

An object being pushed along a smooth surface

Answer 4

A force does work to increase the objects velocity, energy is transferred to kinetic energy equals work done

Question 5

An object being pushed along a rough surface

Answer 5

Force does work to increase an objects velocity and frictional force - kinetic energy gained will be less that work done and energy will be transferred by thermal energy

Question 6

Gravitational Potential Energy

Answer 6

When an object is at a height above the earths surface - when an object is raised it gains GPE but if it is lowered it loses GPE

Question 7

Energy Transfers

Answer 7

• an object lifted above the ground there is work done by lifting force
• objects gains GPE
• if there is a no friction or air resistance when the object stops moving the work done = GPE

Question 8

Kinetic Energy

Answer 8

When an object is moving, this energy depends on both objects mass and velocity - faster it’s going the more KE

Question 9

Energy Conserved

Answer 9

No fraction force then Kinetic Energy lost = Gravitational Potential Energy gained and vice versa

Question 10

Force

Answer 10

Applying to an object may cause it to stretch, compress or bend

Question 11

Elastically Deformed

Answer 11

When it can go back to its original shape - work is done when a force stretches or compresses an object and causes energy to be transferred to elastic energy

Question 12

Inelastically Deformed

Answer 12

When it doesn’t return to its original shape

Question 13

Spring Extensions

Answer 13

Extension of a stretched spring is directly proportional to the load or force applied - stops working when the force is great enough

Question 14

Spring Constant

Answer 14

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

Question 15

Limit of Proportionality

Answer 15

A maximum force above which the graph curves and that extension is no longer proportional force - stiffer the spring = the more elastic energy it has

Question 16

Springs in a Series

Answer 16

1/K = 1/K + 1/K

Question 17

Springs in a Parallel

Answer 17

K = K + K

Question 18

Springs Practical

Answer 18

1) set up apparatus with extra masses then measure mass of each and calculate weight
2) Measure natural length of the spring with a millimetre ruler clamped to the stand - set up at eye level
3) mark the extension of spring
4) add mass and allow it to come to rest, measure new length of spring
5) Repeat
6) Plot force - curve = limit of proportionality

Question 19

Linear Relationship

Answer 19

Straight line means there is a relationship between force and extension - you can use this to find work done as long as it’s not stretched past its limit

Question 20

Elastic Deformation

Answer 20

Formula can be used to calculate the spring’s elastic energy - energy transferred to the spring as it’s deformed

Question 21

Improving Energy in Vehicles

Answer 21

Energy can be transferred, the efficiency of a vehicle depends on the proportion of energy wasted - lower the energy losses the higher the efficiency and less energy is required

Question 22

Idling Losses

Answer 22

• energy wasted when engine is running when the vehicle isn’t moving
• start stop technology reduces energy loss by automatically stopping the engine when stationary

Question 23

Aerodynamic Drag

Answer 23

• drag leads to energy losses as frictional force transfers energy to thermal energy
• effect increases speeds drag reduced by making car aerodynamic
• sports cars allows fluids to flow easily reducing drag, normal cars are more streamline

Question 24

Inertial Losses

Answer 24

• inertia is the measure of how difficult it is to change objects velocity
• adding more mass means more energy is required to change velocity
• lightweight material reduces energy losses

Question 25

Rolling Resistance

Answer 25

• force resists motion of rolling tyres leading to energy loss
• can be reduced by having properly inflated tyres and materials designed to reduce rolling resistance

Question 26

Stopping Distance

Answer 26

Thinking distance + breaking distance
- maximum force is applied by the breaks in order to stop the vehicle in the shortest possible distance
- longer reaction time = high risk of crash
- thinking distance is distance vehicle travels in the drivers reaction time

Question 27

Thinking Distance

Answer 27

• longer your reaction time, longer the thinking distance
• faster you’re going the further you’ll travel during you reaction time

Question 28

Breaking Distance

Answer 28

Distance taken to stop once the breaks have been applied

Question 29

Stopping Completely

Answer 29

Vehicles kinetic energy has to be transferred to heat by friction in the breaks - KE increases with speed so the faster your going further you’ll travel before stopping

Question 30

Mass of Vehicle

Answer 30

KE increases with mass so a vehicle full of people and luggage won’t stop as quickly as an empty one

Question 31

Icy Conditions for a vehicle

Answer 31

Increase the chance of sliding over roads and colliding with other cars

Question 32

Speed Bumps

Answer 32

To encourage people to go slower as they drive because the fast you going the greater the stopping distance has to be

Question 33

Vehicle Safety Features

Answer 33

When a vehicle stops work is done to transfer all this KE to other energy types, force required to stop vehicle depends on a distance over which it’s stopping

Question 34

Safety Features reduce

Answer 34

Forces in collisions and is designed to increase the distance over which work is done, if distance is increased then the force on the passenger decreases

Question 35

Seat Belts

Answer 35

Cars have seat belts designed to stretch when a large force is applied and slows passengers over a longer distance in a crash

Question 36

Air Bags

Answer 36

They inflate as a collision defence to stop hitting the dashboard and increases distance the passenger whilst work is being done

Question 37

Crumple Zones

Answer 37

Areas at front and back of a car which crumple up easily in a collision and increases distance that the whole car moves whilst work is being done to slow car and reduce force