P3: Forces for Transport

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1 P3: Forces for Transport OCR Gateway Additional Science W Richards The Weald School

2 P3a Speed

3 Distance, Speed and Time D Speed = distance (in metres) time (in seconds) S T 1) Freddie walks 200 metres in 40 seconds. What is his speed? 2) Hayley covers 2km in 1,000 seconds. What is her speed? 3) How long would it take Lauren to run 100 metres if she runs at 10m/s? 4) Jake travels at 50m/s for 20s. How far does he go? 5) Izzy drives her car at 85mph (about 40m/s). How long does it take her to drive 20km? 5m/s 2m/s 10s 1000m 500s

4 Distance, Speed and Time D Speed = distance (in metres) time (in seconds) S T 1) Sarah walks 2000m in 50 minutes. What is her speed in m/s? 2) Jack tries to walk the same distance at a speed of 5m/s. How long does he take? 3) James drives at 60mph (about 100km/h) for 3 hours. How far has he gone? 4) The speed of sound in air is 330m/s. Molly shouts at a mountain and hears the echo 3 seconds later. How far away is the mountain? (Careful!) 0.67m/s 400s 300km 495m

5 How speed cameras work Speed cameras work by recording the position of the car at a certain time apart. What is the speed of the trolley in the lab example done below? After 0s After 1.5s

Average Speed It is common to see average speed cameras near roadworks. They work by recording how long you take to cover a certain distance and then working out your average speed.

6 Average Speed It is common to see average speed cameras near roadworks. They work by recording how long you take to cover a certain distance and then working out your average speed. s = u + v 2 t 1) Two cameras are 1km apart and a car takes 50s to travel between them. What was the car s average speed? 2) A car accelerates from 10 to 20m/s for 50s. How far has it gone? 3) How long would it take to travel 10km if you started at a speed of 30m/s and ended up at 50m/s after the 10km? 20m/s 750m 250s

7 Distance-time graphs 2) Horizontal line = 40 4) Diagonal line downwards = Distance (metres) Time/s ) Diagonal line = 3) Steeper diagonal line =

8 40 Distance (metres) Time/s 1) What is the speed during the first 20 seconds? 2) How far is the object from the start after 60 seconds? 3) What is the speed during the last 40 seconds? 4) When was the object travelling the fastest?

9 Distance-time graph for non-uniform motion Distance (metres) Object is accelerating up to here Object is now decelerating Time/s

10 40 Distance (metres) Time/s 1) What was the velocity in the first 20 seconds? 2) What was the velocity between 20 and 40 seconds? 3) When was this person travelling the fastest? 4) What was the average speed for the first 40 seconds? 1.5m/s 0.5m/s s 1m/s

11 P3b Changing Speed

12 Acceleration V-U Acceleration = change in velocity (in m/s) (in m/s 2 ) time taken (in s) A T 1) A cyclist accelerates from 0 to 10m/s in 5 seconds. What is her acceleration? 2) A ball is dropped and accelerates downwards at a rate of 10m/s 2 for 12 seconds. How much will the ball s velocity increase by? 3) A car accelerates from 10 to 20m/s with an acceleration of 2m/s 2. How long did this take? 4) A rocket accelerates from 1,000m/s to 5,000m/s in 2 seconds. What is its acceleration? 2m/s 2 120m/s 5s 2000m/s 2

13 Speed-time graphs 1) Upwards line = 80 4) Downward line = Velocity m/s T/s 2) Horizontal line = 3) Upwards line =

14 80 Velocity m/s ) How fast was the object going after 10 seconds? 2) What is the acceleration from 20 to 30 seconds? 3) What was the deceleration from 30 to 50s? 4) How far did the object travel altogether? T/s 40m/s 2m/s 2 3m/s m

15 Speed-time graph for non-uniform motion Distance (metres) Object s acceleration is increasing Object s acceleration is decreasing Time/s

16 80 Velocity m/s ) How fast was the object going after 10 seconds? 2) What is the acceleration from 20 to 30 seconds? 3) What was the deceleration from 40 to 50s? 4) How far did the object travel altogether? T/s 10m/s 4m/s 2 6m/s m

17 80 Velocity m/s T/s This velocity-time graph shows Coryn s journey to school. How far away does she live? 2500m

18 Speed vs. Velocity Speed is simply how fast you are travelling This car is travelling at a speed of 20m/s Velocity is speed in a given direction This car is travelling at a velocity of 20m/s east

19 Circular Motion 1) Is this car travelling at constant speed? 2) Is this car travelling at constant velocity?

20 P3c Forces and Motion

21 Force and acceleration If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers: Force (in N) = Mass (in kg) x Acceleration (in m/s 2 ) F M A

22 Force, mass and acceleration 1) A force of 1000N is applied to push a mass of 500kg. How quickly does it accelerate? F 2) A force of 3000N acts on a car to make it accelerate by 1.5m/s 2. How heavy is the car? 3) A car accelerates at a rate of 5m/s 2. If it weighs 500kg how much driving force is the engine applying? 4) A force of 10N is applied by a boy while lifting a 20kg mass. How much does it accelerate by? M A 2m/s kg 2500N 0.5m/s 2

23 Stopping a car What two things must the driver of the car do in order to stop in time?

24 Tiredness Too many drugs Stopping a car Thinking distance (reaction time) Too much alcohol Poor visibility Icy roads Tyres/brakes worn out Braking distance Wet roads Driving too fast Total Stopping Distance = Thinking Distance + Braking Distance

25 Stopping Distances This diagram (taken from drivingtestsuccess.com) shows the thinking and braking distances for different speeds. What patterns do you notice? Thinking distance increases linearly Braking distance increases in a squared relationship

26 P3d Work and Power

27 Weight vs. Mass Earth s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N. Weight = Mass x Gravitational Field Strength (in N) (in kg) (in N/kg) M W g 1) What is the weight on Earth of a book with mass 2kg? 2) What is the weight on Earth of an apple with mass 100g? 3) James weighs 700N on the Earth. What is his mass? 4) On the moon the gravitational field strength is 1.6N/kg. What will James weigh if he stands on the moon? 20N 1N 70kg 112N

28 Work done When any object is moved around work will need to be done on it to get it to move (obviously). We can work out the amount of work done in moving an object using the formula: Work done = Force x distance moved in J in N in m W F D

29 Example questions 1. Jessie pushes a book 5m along the table with a force of 5N. She gets tired and decides to call it a day. How much work did she do? 25J 2. Hayley lifts a laptop 2m into the air with a force of 10N. How much work does she do? What type of energy did the laptop gain? 20J, GPE 3. James does 200J of work by pushing a wheelbarrow with a force of 50N. How far did he push it? What type of energy did the wheelbarrow gain? 4m, KE 4. Jack cuddles his cat and lifts it 1.5m in the air. If he did 75J of work how much force did he use? 50N 5. Freddie drives his car 1000m. If the engine was producing a driving force of 2000N how much work did the car do? 2MJ

30 A Practical Example of Doing Work Consider a rocket re-entering the Earth s atmosphere: The rocket would initially have a very high energy. This energy would then due to friction caused by collisions with in the atmosphere. These collisions would cause the rocket to up ( is being done on the rocket). To help deal with this, rockets have special materials that are designed to lose heat quickly. Words work, kinetic, particles, heat, decrease

31 Energy and Power The POWER RATING of an appliance is simply how much energy it uses every second. In other words, 1 Watt = 1 Joule per second E E = Energy (in joules) P = Power (in watts) T = Time (in seconds) P T

32 Some example questions 1) What is the power rating of a light bulb that transfers 120 joules of energy in 2 seconds? 2) What is the power of an electric fire that transfers 10,000J of energy in 5 seconds? 3) Tanner runs up the stairs in 5 seconds. If he transfers 1,000,000J of energy in this time what is his power rating? 4) How much energy does a 150W light bulb transfer in a) one second, b) one minute? 5) Pierre s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a 50 minute physics lesson? 6) Levi s brain, being more intelligent, only needs energy at a rate of about 20W. How much energy would his brain use in a normal day? 60W 2KW 0.2MW 150J, 9KJ 120KJ 1.73MJ

33 An example with cars Citroen Saxo, 60bhp Audi R8, 423 bhp What are the advantages and disadvantages of each car?

34 Power Power (in watts) is the rate of doing work : P = W W t P t Also, using our work done equation: W = FxD P = W = FxD t t therefore P = Fv

35 Random questions on work and power 1) Jordan pushes Tom in the direction of a cliff. If he uses a force of 40N and he moves Tom 10m in 4s calculate the work done and Jordan s power rating. 400J, 100W 2) Chris runs up some stairs and has a power rating of 600W while he does so. If he does it in 5 seconds and his weight is 750N calculate how high the stairs are. 4m 3) A man pulls a block of wood and uses a force of 50N. If the distance travelled horizontally is 5m calculate the work done by the man and his power if the journey lasted 10 seconds. 250J, 25W 50N

36 P3e Energy on the Move

37 Kinetic energy Any object that moves will have kinetic energy. The amount of kinetic energy an object has can be found using the formula: Kinetic energy = ½ x mass x velocity squared in J in kg in m/s KE = ½ mv 2

38 Example questions 1) Shannon drives her car at a speed of 30m/s. If the combined mass of her and the car is 1000kg what is her kinetic energy? 2) Issy rides her bike at a speed of 10m/s. If the combined mass of Issy and her bike is 80kg what is her kinetic energy? 3) Will is running and has a kinetic energy of 750J. If his mass is 60kg how fast is he running? 4) Josh is walking to town. If he has a kinetic energy of 150J and he s walking at a pace of 2m/s what is his mass? 450,000J 4000J 5m/s 75kg

39 Stopping Distances revision Recall the patterns we observed in this data: Thinking distance increases linearly Braking distance increases in a squared relationship

40 Stopping a car What happens inside the car when it stops? In order to stop this car the brakes must do work. This work is used to reduce the kinetic energy of the vehicle and the brakes will warm up this is why the braking distance depends on speed 2

41 An example question This car can apply a maximum braking force of 10,000N. If the car s mass is 1000Kg how far is its stopping distance when it is travelling at a speed of 15m/s (roughly 30mph) and 30m/s (roughly 60mph)? 15m/s = 11.25m stopping distance 30m/s = 45m stopping distance (4 times greater)

42 Different ways of fuelling cars What are the advantages and disadvantages of each of the following fuels?

43 Fuel consumption How do the following features help or hinder fuel economy? Having an aerodynamic shape Having a roof box Having a deflector Having a window open

44 P3f Crumple Zones

45 Momentum Any object that has both mass and velocity has MOMENTUM. Momentum (symbol p ) is simply given by the formula: P Momentum = Mass x Velocity (in kgm/s) (in kg) (in m/s) M V What is the momentum of the following? 1) A 1kg football travelling at 10m/s 2) A 1000kg Ford Capri travelling at 30m/s 10kgm/s 30,000kgm/s 3) A 20g pen being thrown across the room at 5m/s 4) A 70kg bungi-jumper falling at 40m/s 0.1kgm/s 2800kgm/s

46 Force and momentum Newton s second law of motion says that the force acting on an object is that object s rate of change of momentum. In other words Force = Change in momentum (in N) Time (in s) Also called impulse (in kgm/s) F mv T For example, Rooney takes a free kick by kicking a stationary football with a force of 40N. If the ball has a mass of 0.5kg and his foot is in contact with the ball for 0.1s calculate: 1) The change in momentum of the ball (its impulse), 2) The speed the ball moves away with

47 Example questions 1) Paddy likes playing golf. He strikes a golf ball with a force of 80N. If the ball has a mass of 200g and the club is in contact with it for 0.2s calculate a) the change in momentum of the golf ball, b) its speed. 2) Courtney thinks it s funny to hit tennis balls at Kit. She strikes a serve with a force of 30N. If the ball has a mass of 250g and the racket is in contact with it for 0.15s calculate the ball s change in momentum and its speed. 3) Tom takes a dropkick by kicking a 0.4kg rugby ball away at 10m/s. If his foot was in contact with the ball for 0.1 seconds calculate the force he applied to the ball. 4) Jenny strikes a 200g golf ball away at 50m/s. If she applied a force of 50N calculate how long her club was in contact with the ball for. 16Kgm/s, 80m/s 4.5Kgm/s, 18m/s 40N 0.2s

48 How do air bags and crumple zones work? Safety features mv Basically: F T 1) The change in momentum is the same with or without an airbag 2) But having an airbag increases the time of the collision 3) Therefore the force is reduced

49 Car Safety Features These objects all help reduce injury by basically absorbing energy. Cars also have ABS brakes which prevent them from skidding by automatically pumping off and on to avoid the brakes locking.

50 P3g Falling Safely

51 Introduction to Forces A force is a push or a pull. Some common examples: Weight (mg) pulls things towards the centre of the Earth Air resistance/drag a contact force that acts against anything moving through air or liquid Friction a contact force that acts against anything moving Upthrust keeps things afloat

52 Examples of Air Resistance

53 Balanced and unbalanced forces Consider a camel standing on a road. What forces are acting on it? Reaction These two forces would be equal we say that they are BALANCED. The camel doesn t move anywhere. Weight

54 Balanced and unbalanced forces What would happen if we took the road away? Reaction Weight

55 Balanced and unbalanced forces

56 Balanced and unbalanced forces 1) This animal is either or moving with 2) This animal is getting 3) This animal is getting. 4) This animal is also either or moving with.. Words - Stationary, faster, slower or constant speed?

Complete these sentences Summary If an object is stationary and has NO resultant force on it the object will If an object is stationary and a resultant force acts on it the object will If an object

57 Complete these sentences Summary If an object is stationary and has NO resultant force on it the object will If an object is stationary and a resultant force acts on it the object will If an object is already moving and NO resultant force acts on it the object will If an object is already moving and a resultant force acts on it the object will accelerate in the direction of the resultant force continue to stay stationary continue to move at the same speed and the same direction accelerate in the direction of the resultant force

58 Terminal Speed Consider a skydiver: 1) At the start of his jump the air resistance is so he downwards. 2) As his speed increases his air resistance will 3) Eventually the air resistance will be big enough to the skydiver s weight. At this point the forces are balanced so his speed becomes - this is called TERMINAL SPEED Words increase, small, constant, balance, accelerates

59 Terminal Speed Consider a skydiver: 4) When he opens his parachute the air resistance suddenly, causing him to start. 5) Because he is slowing down his air resistance will again until it balances his. The skydiver has now reached a new, lower. Words slowing down, decrease, increases, terminal speed, weight

60 Velocity-time graph for terminal velocity Velocity Speed increases Terminal velocity reached Parachute opens diver slows down New, lower terminal velocity reached Time Diver hits the ground

Acceleration due to Gravity Notice that the skydiver s weight didn t change at any point. Or did it? In reality, every object that is close to the has the same gravitational.

61 Acceleration due to Gravity Notice that the skydiver s weight didn t change at any point. Or did it? In reality, every object that is close to the has the same gravitational. However, if you drop an object from the top of Mt Everest its acceleration will be slightly! Also, if you take out, objects would fall with the same acceleration (like the skydiver on the ). Words acceleration, Earth, moon, air resistance, smaller

62 P3h The Energy of Games and Theme rides

63 Gravitational Potential Energy To work out how much gravitational potential energy (GPE) an object gains when it is lifted up we would use the simple equation GPE = Mass x Acceleration of free-fall x Change in height (Joules) (newtons) (=10N/kg) (metres) (Remember - W=mg) GPE mg H

64 Some example questions How much gravitational potential energy have the following objects gained?: 1. A brick that weighs 10N lifted to the top of a house (10m), 2. A 1,000kg car lifted by a ramp up to a height of 2m, 3. A 70kg person lifted up 50cm by a friend. 100J 20KJ 350J How much GPE have the following objects lost?: 1. A 2N football dropping out of the air after being kicked up 30m, 2. A 0.5N egg falling 10m out of a bird nest, 3. A 1,000kg car falling off its 200cm ramp. 60J 5J 20KJ

65 Energy changes for a skydiver Recall our skydiver: If the skydiver has reached terminal speed explain what happens to his 1) Kinetic energy 2) Gravitational potential energy while he is falling.

66 Understanding Kinetic Energy KE = ½ mv 2 If the mass of the object is doubled what effect would this have on the object s kinetic energy? If the speed of the object is doubled what effect would this have on the object s kinetic energy?

67 1) Electrical energy is transferred into gravitational potential energy Roller Coasters 3) Kinetic energy is transferred back into gravitational potential energy 2) Gravitational potential energy is transferred into kinetic energy

68 Using conservation of energy when dropping objects If I drop this ball 1m how fast will it be going when it hits the floor? Use GPE at top = Kinetic energy at bottom mgh = ½mv 2 gh = ½v 2 h = v2 2g v 2 = 2 x 10 x 1 1m v 2 = 20 v = 4.5m/s

69 An example question If the height of the drop was 100m and assuming there was a 100% conversion from gravitational to kinetic energy, how fast was the roller coaster car moving at the bottom of the ramp?

11/05/2018 Physics Paper 2

11/05/2018 Physics Paper 2 Physics Paper 2 P8 Forces in Balance Vectors and Scalars Vectors are things that have a size and direction. They can be represented by an arrow. The length of the arrow is the magnitude (size) and the