Forces and Motion

Question 1

thinking distance

Answer 1

distance a vehicle will travel from seeing the hazard to applying the brakes

Question 2

stopping distance

Answer 2

distance a vehicle will travel between seeing the hazard to coming to a complete stop

Question 3

braking distance

Answer 3

distance a vehicle will travel between fully applying the brakes to coming to a complete stop

Question 4

thinking, braking and stopping distance

Answer 4

stopping distance = thinking distance + braking distance

Question 5

distance =

Answer 5

speed x time

Question 6

how to find acceleration from v/t graph

Answer 6

gradient of the line

Question 7

how to find total distance travelled from a v/t graph

Answer 7

total area underneath the line

Question 8

negative gradient on v/t graph

Answer 8

deceleration

Question 9

negative gradient on a d/t graph

Answer 9

returning to start/moving backwards

Question 10

acceleration

Answer 10

change in velocity / change in time

Question 11

brakes use…..to slow down a vehicle

Answer 11

friction

Question 12

force, mass and acceleration

Answer 12

force = mass x acceleration

Question 13

braking force =

Answer 13

mass x deceleration

Question 14

when braking: work done =

Answer 14

braking force x braking distance

Question 15

work done =

Answer 15

force x displacement

Question 16

kinetic energy =

Answer 16

1/2 x mass x velocity^2

Question 17

momentum =

Answer 17

mass x velocity

Question 18

measurement of momentum

Answer 18

kg m/s

Question 19

conservation of momentum

Answer 19

yes
in a closed system with no external forces acting, the total momentum before a collision (or explosion) is the same as the total momentum after a collision

Question 20

define explosion

Answer 20

when two objects begin stationary (0kgm/s) and are thrown apart in opposite directions with equal momentum

Question 21

closed system

Answer 21

physical system that does not exchange matter with the surroundings but is still able to exchange energy

Question 22

find velocity in an explosion =

Answer 22

m1 x v1 = m2 x v2
mass of component 1 x velocity of component 1 = mass of component 2 x velocity of component 2

Question 23

elastic collision

Answer 23

both energy and momentum are conserved

Question 24

inelastic collision

Answer 24

momentum is conserved but kinetic energy is not

Question 25

change in momentum =

Answer 25

F = change in momentum / change in time

Question 26

safety features of a car

Answer 26

* crumple zone * seat belt * airbag

Question 27

crumple zone

Answer 27

* designed to absorb impact energy during a collision * creates more vehicle damage but decreases damage to passengers

Question 28

seat belt

Answer 28

* the **webbing** of a seatbelt stretches, which absorbs some of the energy in an impact * reduces the risk of fatal injury by 45%

Question 29

airbag

Answer 29

* inflatable cushions built into a vehicle that protect occupants from hitting the vehicle interior or objects outside the vehicle * reduces the risk of fatal injury by 61%

Question 30

centre of gravity

Answer 30

a ‘theoretical’ point on an object where all of the weight appears to be concentrated.

Question 31

how to find centre of gravity on irregular objects

Answer 31

* draw two lines from seperate suspension points * where the two lines cross is the centre of gravity

Question 32

centre of gravity in suspended objects

Answer 32

CoG always found below the point of suspension

Question 33

centre of gravity in standing objects

Answer 33

CoG always found above the base of the object or the object will topple

Question 34

what makes objects fall over

Answer 34

when the line of action from the centre of gravity lies outside the base of the object

Question 35

how to make an object more stable

Answer 35

* lower the centre of gravity * increase the width of the base

Question 36

moment

Answer 36

a turning effect that comes from a force being applied a perpendicular distance from a pivot

Question 37

moment =

Answer 37

force x distance (measured in N)

Question 38

principle of moments

Answer 38

if the clockwise moments and the anticlockwise moments are equal, the system will be in equilibrium if not, the system will rotate in the direction of the greatest moments

Question 39

perpendicular force from a pivot

Answer 39

a line from a pivot which meets the line of action of a force at 90°

Question 40

uses of turning forces

Answer 40

* open doors * unscrew bolts * balance a seesaw * prise things open with a crowbar

Question 41

factors affecting stopping distance

Answer 41

* weather * road condition * visibility * tiredness of driver

Question 42

Newton's Third Law of Motion

Answer 42

every action has an equal reaction

Question 43

support forces

Answer 43

S1 + S2 = W + w

Question 44

how does a falling object reach a terminal velocity

Answer 44

* Object has weight or there is a downward force * So it accelerates * there is air resistance opposing the downwards force * air resistance increases as speed increases * eventually drag = weight * (hence) resultant force is zero * (hence) object travels at constant speed;

Question 45

Hooke's law

Answer 45

The extension of a spring is directly proportional to the force applied, provided that the limit of proportionality is not exceeded

Question 46

pressure =

Answer 46

force / area