P2 Exam questions

The following presentation contains the questions that have come up in the past papers over the last few years If you learn the answers (in bold) to these questions and can apply them to similarly worded questions you will do really well in the exam!

1. Must be able to describe that unbalanced forces produce acceleration What do the arrows represent? Describe the motion of this car: The size and the direction of forces Accelerating to the left Because the resultant force is to the left

2. Be able to calculate acceleration (acceleration equation) A car is travelling at 10 m/s and accelerates to 25m/s in 5 seconds. Choose the correct equation and calculate the acceleration. Acceleration = change in velocity / time Acceleration = (25-10)/5 Acceleration = 3 m/s²

3. Difference between velocity and speed Define velocity and speed Speed is a scalar quantity with magnitude only Velocity is a vector quantity so has magnitude and direction Speed is the distance travelled in a certain time Velocity is the speed in a given direction

4. Be able to calculate force (F=ma) If the mass of the car in question 2 is 1200kg what driving force is necessary to accelerate it. F=ma Force = 1200 x N

5. Calculating weight Gravity = 10m/s 2 What is the weight of an object of 20kg? Weight = mass x gravity Weight = 20 x 10 Weight = 200N

Stopping distances The stopping distance of a vehicle is the distance it travels until it stops. Stopping distance = thinking distance + braking distance

6. What is meant by braking distance Braking distance is the distance travelled after the brakes have been applied to the vehicle until it stops

7. What is meant by thinking distance Thinking distance is the distance travelled from when the driver sees something that must be stopped for until they apply the brakes. It is the distance travelled during the reaction time of the driver

8. Factors affecting Stopping distances Factors affecting thinking distance Factors affecting braking distance Alcohol / drugsWeather conditions (icy / wet roads) TirednessPoor road conditions Distractions (mobile phones etc) Poor brake conditions Increased Speed

9. Calculation of work done The force from the brakes on a car convert kinetic energy into ___________? The force on a car is 12kN and it stops in 5 metres. What is the work done by the brakes? heat energy W = F x d W = x 5 W = 60000J

10. What is a regenerative braking system in a hybrid car? A regenerative braking system charges the hybrid/electric car’s battery while it is braking. 11. Why are they useful? It is useful as it means that the car will not have to charge up the battery as often and will have a longer range when using the electric motor.

12. Using distance time graphs to find speed (and maximum/minimum speed from gradient calculation) What is the speed between 0 and 5 seconds? Is this different from the speed between 5 and 6 seconds? On the return journey the speed isn’t constant. At what time between 11 to 18 seconds is the speed the least? Gradient = 8/5 1.6m/s No – the gradient is the same Where the gradient is the least steep At 14 seconds

13. Be able to describe that action and reaction forces are the same A car travels at a constant speed. The tyres cause a traction force of 50 N. What is the size of the frictional force? Explain. 50N For a constant speed there is no resultant force

14. Calculation of GPE Gravity = 10m/s 2 A book of 0.5kg is raised 2 metres. What is the gravitational potential energy of the book? GPE = mgh GPE = 0.5 x 10 x 2 GPE = 10J

15. Converting GPE in KE The book falls to the ground. How much kinetic energy does it have just before it hits the floor? It has the same as the maximum GPE as long as it is not lost because of air resistance as heat or sound 10J

16. Work done against friction is wasted as heat which is transferred to the surroundings e.g. A cyclist loses as they travel down a hill and gains. As they apply the brakes this energy is changes into as the bike stops. GRAVITATIONAL POTENTIAL ENERGY KINETIC ENERGY HEAT/THERMAL ENERGY

17. Calculating speed from KE equation KE of a ball of mass 2kg is 100J. What speed is it travelling at? KE = ½ m v² v =  (2xKE/m) v =  ((2 x 100) / 2) v =  100 v = 10m/s

18. Finding acceleration and distance from velocity-time graphs What is the acceleration from 0- 4 seconds? What distance has been travelled from A to C? Gradient = 8/4 Acceleration = 2m/s² Distance = area under the graph Rectangle = 5.2 x 10 = 52m Triangle = 3/2 x 10 = 15m Total distance = = 67m

19. Why things become statically charged and forces between charged objects Explain why a balloon gets statically charged when it is rubbed on somebody’s hair. Why does a balloon that is charged up stick to a wall? What would happen if you brought 2 balloons that are charged up in a similar way together? Friction causes electrons to be rubbed from one surface to the other. This means that one object has more electrons than protons and so is charged negatively The other object has more protons than electrons and so is charged positively A balloon that is charged negatively will Repel negative electrons away from the surface of a wall This will leave positive protons that it is attracted to They would repel away from each other since similar charges repel

20. Hooke’s Law Define Hooke’s Law Hooke’s Law states that the extension of a spring is directly proportional to the Force applied until it reaches the elastic limit Find the spring constant from the graph. The spring constant is found from the gradient of a force extension graph: Gradient = 10 / 0.2 = 50 N/m The elastic limit isn’t shown on the graph. What is meant by the elastic limit and what would happen to the shape of the graph if the spring is extended beyond it? The elastic limit is the limit of proportionality. Past this point the line on the graph is no longer straight and the spring would no longer go back to its original length. The graph would curve and flatten past the elastic limit

21. Finding Resistance from a graph and data Use calculations to show how the resistance of a bulb vary with increased potential difference. R=V/I At A the resistance = 1/7 = 0.14 Ω At D the resistance = 4/13 = 0.31 Ω So this shows that as the voltage increases the resistance increases in a bulb 22. Explain the shape of the graph As the voltage increases the current increases As the current increases the temperature increases The increasing temperature makes the resistance increase as ions vibrate more in the wire

23. Drawing circuits (measuring current and pd – resistance of ammeters and voltmeters) and why we need to include a variable resistor Draw a circuit that could be used to investigate the changing resistance of a bulb. Include a variable resistor in your circuit and explain why it is important. A variable resistor must be included to be able to vary the voltage across the bulb to get more than 1 result enough results to see a pattern

24. Define electric current Electric current is the amount of charge flowing past a point in a given time

25. Calculation of charge If a current of 2.5A flows through a resistor is a minute how much charge has passed through it? Q = I x t Q = 2.5 x 60 Q = 150 C

26. Define potential difference Potential difference is the energy transferred per charge

27. Circuit symbols for thermistor, LDR, diode, variable resistor thermistor, LDR, diode variable resistor

28. How resistance changes with temperature and light Draw a sketch graph of resistance (y axis) and temperature (x-axis) for a thermistor Draw a sketch graph of resistance (y axis) and light intensity (x-axis) for an LDR

29. Calculation of electrical power A filament lamp has a current of 3A and a potential difference of 12V across it. What is the power of the lamp? Power = current x p.d Power = 3 x 12 Power = 36W

30. Using graphs to find data to calculate power A student does an experiment and gets the following results of varying potential difference and current for a bulb. Use the graph to find the power of the bulb at 3.5A Power = current x p.d. Power = 3.5 x 0.1 = 0.35W

31. Sources or background radiation State sources of background radiation. Sort them into natural and manmade sources. Natural Cosmic rays, rocks – building materials, soil, plants, animals Man made Medical uses of X-rays and gamma rays Uses of Nuclear fuels in power stations

32. Comparing dose and exposure from data given Explain whether you think it is safe for an airline pilot to fly 13 return flights from LA to New York. Each flight receives dose of 40 microSv 13 return flights would be 26 flights 26 x 40 = 1040 microSv The recommended limit is 1000 and 1040 is higher than this so it is not safe for a pilot to fly 13 of these return flights.

33. Nuclear notation and reactions Explain what A, Z and X mean below: A is mass number (number of neutrons + number of protons) Z is proton number X is the symbol for the element

34. Half-life from a graph Find the half-life of carbon 14 from the graph below. Show how you have found it. The half life is 5700 years

35. Comparison of light bulbs using data 36. Life cycle of star Look at 6 mark booklet

37. Energy transfers in a power station How do nuclear power generators work? Describe the energy transfers in a nuclear power station. Fission produces heat energy Heat energy heats water and turns it to steam Steam turns a turbine The turbine turns a generator and makes electricity

38. What is the fuel in nuclear reactors? Uranium 235 (or Plutonium 239)

39. What is absorbed by the Uranium nucleus in nuclear fission? A neutron 40. What do control rods do? Control rods are made of boron and absorb neutrons so that chain reactions can be slowed and controlled

41. Define Nuclear fusion and describe where it happens naturally Nuclear fusion is the fusing together of hydrogen nuclei into helium nuclei. Since hydrogen consists of 1 positively charged proton Hydrogen nuclei repel each other So to fuse them they must have a massive amount of kinetic energy The amount of heat necessary to generate this amount of kinetic energy occurs naturally in stars and this is where fusion happens

42. How are elements formed in stars? Large stars fuse heavier nuclei together to form heavier elements 43. Explain how elements heavier that iron are made and scattered across the universe When stars explode as supernovae enough heat is produced to fuse very heavy elements together. This forms all the naturally occurring elements in the universe and as part of the explosion these elements are scattered around the universe

44. What does conservation of momentum mean? The sum of the momentum before a collision or explosion is the same as the sum of the momentum after the collision or explosion

45. Calculate velocity from conservation of momentum 2 stationary ice skaters push away from each other. How much momentum is there in total before they push away from each other? zero How much is there afterwards? zero One moves to the right with a velocity of 4m/s and the other moves away to the left. The one on the right has a mass of 30kg and the one on the left has a mass of 50kg, what is their velocity? Draw a diagram if this helps. Momentum to the right = 30 x 4 = 120 kgm/s Momentum to the left must equal -120 kgm/s so velocity = -120/50 = -2.4m/s i.e. the one on the left has a velocity in the opposite direction of 2.4 m/s

46. Structure of electrical power leads There are 3 wires in an electrical lead, what are they, what is each ones’ job and what colour are they? Live – p.d. is 230V Neutral – p.d. stays very close to 0V Earth – takes any excess charge away from a faulty appliances

47. Define of AC and DC and sketch what they would look like on a CRO screen. AC is alternating current and DC is direct current (DC is the flat line – AC is the other one)

48. Calculation of frequency of AC. If the time base is set to 5ms what is the frequency of the alternating current below. Is this what you would expect? Time period = 4 x 5ms = 20ms 20ms = 20/1000 = 0.02 s Frequency = 1/T f = 1/ 0.02 f = 50 Hz The frequency of household AC is 50Hz so this is what I’d expect

49. Compare the way an RCCB works to a fuse and explain the advantages An RCCB compares the current flowing between the live and neutral wire The sensitivity of the RCCB can be changed and if the current is too high the electromagnetic switch triggers and the circuit is broken A fuse is a thin piece of wire that has a specific melting point If the current is too high for the fuse the wire melts and breaks the circuit There are 2 advantages to RCCBs. They can be reset and the sensitivity can be varied There is one advantage of a fuse in that they are very cheap.