acceleration = change in speed (m/s) time (s)

Example: What is the acceleration of a rocket if itaccelerates from 20m/s to 100m/s in 2 seconds?Answer a = change in speed time = 100-20 = 80/2 = 40m/s/s 2

AccelerationThis is the change in speed per second. Theunits of acceleration are m/s/s

Typical Questions1) What is the distancetravelled by car A? 500m

2) What is the speed of carA?s =d/t = 500/20 = 25m/s

3) What is the distancetravelled by car B? 200m

4) What is the speed of carB?s = d/t = 200/25 = 8m/s

time in seconds

stationary

car B

car A

stationary

distance(m)

constantspeed

constantspeed

Distance-Time graph for two cars500

400

300

200

100

10 20 30

time in seconds

Typical Questions1) What is the maximum speedof the car? 30m/s2) What is the car's accelera-tion?acceleration = change in speed time =30/10 = 3m/s/s

speed(m/s) constant speedconstant acceleration

Speed - Time graph for a car

10

20

30

5 10

Calculating distancefrom a Speed-time

graphThis is done by calculating thearea under the graph.The distance travelled by thecar while it is accelerating isthe area of a triangle.area of triangle = 1/2 b x h =1/2 x 10 x 30 = 150m

Stopping Distance stopping = thinking + brakingdistance distance distanceSpeed(or velocity) = distance (m)(m/s) time (s)

Example: What isthe distance travelledin 30 seconds by acar travelling with avelocity of 30m/s?answer: d = s x t = 30 x 30 = 900m

d

s t

a t

chs

P3:Higher Physics of Transport

Thinking distance is the distance you go while reacting. It is affected byalcohol, drugs and speedBraking distance is the distance travelled once the foot is on the brakeand is affected by how hard the brakes are pressed (the harder the pedalis pressed the more the friction between the brake pad and wheel),speed, weather, road and tyre conditions. Anything which reducesfriction will increase braking distance.

Example: What force is needed to makea 100000 Kg boat accelerate at 0.5m/s2?answerF = ma = 100000 x 0.5 = 50000N

acceleration = force(N) (m/s2) mass(Kg) a = F

m

F

a m

A big force on a smallmass gives a very bigacceleration

Written by M J Bradley

Strength of Earth's Gravitya = f/m so g = W/mSo weight, W = mg

Example How heavy is a 100kg man on Earth?answer W = mg = 100 x 10 = 1000N

g is the strength ofEarth's gravity. It isabout 10N/kg. On themoon it is 1.6N/kg

The Link between Force,Mass and Acceleration

Terminal SpeedObjects fall to the groundbecause of the pull of gravity.When an object falls on Earthit first gets faster (accelerates)then it reaches a steady speedjust like when a cyclistreaches top speed on a bike.This maximum speed is calledthe terminal speed and ithappens when the forces onan object become balancedThe forces become balancedbecause the air drag increases.

terminal velocity (or speed)

velocity m/s

time (s)

weight

air dragThe weight and airdrag forces arebalanced at theterminal speed

Gravitational Potential EnergyThis is the energy something has due to it heightabove the ground

Potential Energy = mass x g x height (J) (kg) (m)g is the acceleration due to gravity = 10 m/s2

Example What is the potential energy of a steel girder of mass 1000kg when a crane lifts it to aheight of 100m.?PE = m x g x h = 1000 x 10 x 100 = 1000000J

Kinetic EnergyAnything which moves has kinetic energy. Ifan object has a big mass and a high speed ithas a very big kinetic energy

kinetic energy = 1/2 x mass x velocity2 (J) (kg) (m/s)

Examples: (1) What is the Kinetic energy of a 100 000kg train moving with a velocity of 30m/s?answer: KE = 1/2 x m x v2 = 1/2 x 100 000 x 302 = 1/2 x 100 000 x 900 = 45000000J

Transfer of Potential and Kinetic Energy

A B

C

The law of energy conservation is that energy isnever destroyed but can be transferredA - The ball has kinetic and potential energyB- The ball has maximum potential and mini-mum kineticC - On the point of impact the ball has maximumkinetic energy and zero potential energy

PowerPower is how quickly work is done. If a machine does a lot ofwork in a short space of time it has a high power. It is measuredin joules per second which scientists call watts (W)

Power = work done (J)(W) time (s)

Example: The power of a machinethat does 2000J of work in 2s isP = WD = 2000 = 500W t 2

WD

WorkWork is done when a force moves an object through a distance.Work is a transfer of energy. E.g. lifting a book chemical potentialenergy in muscles is changed to gravitational potential energy

Work Done = force x distance (J) (N) (m)

Example The work done by a carpulling a trailer with a force of 200Nthrough a distance of 1000m isWD = F x d = 200 x 1000 = 200000J

WD

F d P t

PE

m x g x h

All gravitationalpotential energy, nokinetic

kinetic energy ismaximum and thepotential energy iszero

The kinetic energy istransferred back topotential energy

WEDNESFIELDHIGH SCHOOL

EXTREME RIDES

If the brakes are neverapplied will this ridelast forever?What will happen?

Imagineyou aretowed up tothe top of ahigh slopeand thecable isreleasedfrom thecarriage

CrashesIn any collision kinetic energy needs to be absorbed andtransferred to other forms of energy. Car brakes transferkinetic energy to heat.Crumple zones, car bumpers, air bags absorb energyslowly and reduce the impact forceSeat belts keep the occupants in their seat. In a crashthey are best replaced because their is a danger of thembeing permanently stretched and weakened - dangerous ina further crash

1) speed = ?2) What is the distance travelled by a car in 20s if travelling at 20m/s?3) acceleration = ?4) What is the acceleration of a car if it accelerates from 10m/s to 30m/s in4s?5) To make something accelerate there must be an ______ force actingupon it6) The bigger the resultant force acting on an object the _______ theacceleration. The smaller the mass the ______ the acceleration. For aracing car the best combination for high acceleration is ______ mass and_____ thrust from the engine.7) What equation links force, mass and acceleration?8) What is the acceleration of a car if the force from the engine is 8000Nand the mass is 1000 Kg?9) What is the force required to make a 1000 kg car accelerate at 9m/s2?10) When a falling object reaches its terminal speed the forces on it are________11) Sketch a graph of speed against time for a falling object starting fromrest (zero speed).

12) Three safety features of cars are.......13) An air bag reduces the force on a driver during a crash because................[3]14) Stopping distance = ________ + _________15) What is meant by braking distance?16) What things increase braking distance?17) What is meant by thinking distance?18) What things increase thinking distance?19) What is the thinking distance of a driver if the reaction time is 0.5s andthe speed is 40m/s?20) What is the stopping distance of a car if the thinking distance is 15mand the braking distance is 75m?21) Use the graph to describe the motion of a bus in terms of speed andacceleration

22) What is the acceleration of the bus?22b) What is the distance travelled while accelerating23) For how long was it at steady speed?24) What was the deceleration?25) Use the graph below to describe the motion of a cyclist in terms ofspeed

26) What was the cyclists' speed in the first 5 seconds?

spee

d (m

/s)

time (s)

20

4 1618

dist

ance

(m)

time (s)

30

5

1) distance/time2) d = sxt = 20 x 20 = 400m3) acceleration = speed change/time4) a = chs/t = 20/4 = 5 m/s2

5) unbalanced (resultant)6) bigger bigger small big

7) a = f/m8) a = f/m = 8000/1000 = 8m/s2?

9) f = ma = 1000 x 9 = 9000N10) balanced

12) seat belts, air bags, crumple zones13) increase the time for the collision,reducing the deceleration and reducingthe force because f = ma14) thinking distance + braking distance15) distance travelled with foot on brake16) wet weather, poor brake condition, 17) distance travelled while reacting18) alcohol, drugs, tiredness19) d = sxt = 40 x 0.5 = 20m20) sd = td + bd = 15 + 75 = 90m

21) accelerates then steady speed thenrapid deceleration

22) a = chs/t = 20/4 = 5 m/s222b) area under graph =0.5bh = 0.5 x 4 x 20 = 40m23) 12s24) a = chs/t = 20/2 = 10m/s2

25) steady speed for 5s then stationary

26) s = d/t = 30/5 = 6m/s

time

spee

d

UNIT P3 FORCES AND MOTIONFOLD

27) Work is a measure of _______ transfer28) Work = _______ x _______ or wd = _____29) How much work is done by a 1000N man climbing stairs 10mhigh?30) Power is the rate at which ________ is done31) If a machine does a lot of work in a small amount of time it has a________ power. If it does little work in a long time (like some ofyou) it has a ______ power. One joule per second is one _______32) Power = ______ or p = 33) What is the power of a machine if it does 10000J of work in 10s?34) Gravitational potential energy is the__________ energy of anobject which is ________ up and is equal to the amount of ______done to get it there35) Potential energy = mass x _____ x ______ or PE = ________36) What is the potential energy of a 10Kg mass 20m above theground?( take g = 10m/s2)37) Moving objects have ________ energy38) Kinetic energy = 0.5 x mass x _________ or KE = ________39) What is the kinetic energy of a 1000Kg car travelling at 20m/s?

40) Energy cannot be _________ but can be __________ to otherforms41) A playground slide converts _________ energy to ________energy42) The brakes on a car do work to stop it. _______ energy istransferred to ________ energy.43) A ball has 50J of potential energy. If it is dropped how muchkinetic energy does it have the moment before it hits the ground?44) If a car has 200000J of kinetic energy what distance will it take tostop if the braking force is 4000N?45) At the top of the ride below Mr Bradley's _______ energy is at a______ and his kinetic energy is _______. As he falls potentialenergy is transferred to _______. His kinetic energy is at a maximumat the ______ of the ride. This kinetic energy is then transferred backt o _____ _ energy.

27) energy28) force x distance , wd= fd29) wd = fd = 1000x10 = 10000J

30) work31) high , low, watt

32) Power = work done /time, p = wd/t33) p = wd/t = 10000/10 = 1000w

34) stored, high, work

35) = mass x gravity strength x heightPE = mgh36) PE=mgh = 10x10x20 = 2000J

37) Kinetic38) 0.5 x mass x velocity2

39) KE = 0.5mv2 = 0.5x1000x 202

= 0.5x1000x400 = 200000J40 ) created or destroyed, transferred

41) potential, kinetic

42) kinetic, heat43) 50 J44) Work done to stop = ke of carfd = KE so d = KE/f = 200000/4000 = 50m45) potential, zero, kinetic , bottom,potential

WEDNESFIELDHIGH SCHOOL

EXTREME RIDES

P3 TEST: Transport Physics

Name ___________________________ Form:___________

15_ car A mass 1000kg speed in m/s10_

5__

15_ car B mass 1500kg speed in m/s10_

5__

time in seconds 0.1 s 0.2 stime in seconds

2) New cars are tested in crashes.Scientists study the results. Two cars crashinto a wall. Look at these graphs(a) Car A takes 0.2 s to stop during thecrash. Calculate the acceleration of car A duringthe crash.________________________________________________________________________________________________________________________________________Answer______________m/s2 [3]

(c) After the crash car B is more damaged. Car B must have had much greater forces on it during thecrash. Explain why.___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________[3]

0 0

(b) Calculate the distance car A travels during the crash.________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________Answer___________________m [3]

1(a) Nick thinks cars travel to fast near his school. He calculates the speeds of cars as they movepast the school. Write about the experiment Nick did to calculate the cars speedIn your answer include(i) what equipment he used(ii) what measurements he took

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

________________________________________________________________________________________[4]

4) Five cars travel along the motorway. They go through two tunnels. Both tunnels are the samelength.They go through tunnel A first. Look at the results.

(a) Which cars increase their speeds?__________________________________________________________________________________[1](b) Which car has the highest acceleration?__________________________________________________________________________________[1](e) Tunnel A is 200m long. Calculate the speed of the Mini through tunnel A__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________[2]

Describe the factors that will increase stopping distance______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________[5]

(d) Elaine wants to buy a car. She has a choice ofthree engines. All the cars have the same mass. Eachengine produces a different maximum force.Look at the information in the table.

(i) The GSi model has the highest acceleration. Explainwhy._____________________________________________________________________________________________________________________________________________________________________[2](ii) The GSi model now pulls a caravan. Its maximum acceleration is now 2.5m/s2.Calculate the mass of the caravan. ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________[4]_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

S model GS model GSi model

Enginecapacity

1.3 litres 1.6 litres 2.0 litres

Maximumforce

2500N 3000N 4000N

Mass 1000Kg 1000Kg 1000Kg

car movingat 30 km/h thinking distance braking distance

car hasstopped

Car Time to pass through tunnel Ain seconds

Time to pass through tunnel Bin seconds

Astra 6 8Focus 6 3Golf 7 3Mini 5 5Saxo 10 11

(3) Look at the diagram on stopping distances for cars.

1.1m

5) Barry must lift some heavyweights onto a lorry. Eachweight is 600N and he mustlift them 1.1m onto the lorry.(a) How much work is donelifting one weight onto thelorry?________________________

_______________________[2]

______________________________________________________________________________________________________________________________________________________________________[4]b) How much work is done lifting all 3 weights onto the lorry? __________________________________________________________________________________________________________________[1]

c) If it takes Barry 100 seconds to load the lorry with all three weights what is his average power?________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________[4]

6) Look at the picture of the ball. It is stationary on the edge of a tablei) What is the gravitational potential energy of the ball? (take g as10m/s2)__________________________________________________________________________________________________________________[4](ii) If the ball is stationary what is its kinetic energy?_______________________________________________________[1]

(iii) Describe what happens to the potential and kinetic energy of the ball as it falls to the ground________________________________________________________________________________________________________________________________________________________________________[2](iv) What is the kinetic energy of the ball just as it hits the ground? ___________________________________________________________________________________[1]

7a (i) A car has a mass of 1000kg and a speed of 20m/s. What is its kinetic energy?________________________________________________________________________________________________________________________________________________________________________[4](ii) The brakes provide the force to stop the car. As the car stops what type of energy is the kineticenergy converted to? __________________________________________________________ [1](iii) If the brakes provide a force of 5000N how far does the car travel while stopping? [4]______________________________________________________________________________________________________________________________________________________________________

speed braking distance0 01 22 83 184 325 50

(b) Look at this data of the braking distance of acar Describe in detail how braking distance changeswith speed. Use the kinetic energy equation toexplain your description______________________________________________________________________________________________________________________________________________________________________________[3]

1.5m

mass = 0.1Kg