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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?
The size and the direction of forces
Describe the motion of this car:
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 3
• 3600 N
5. Calculating weight
• Gravity = 10m/s2
• 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
Alcohol / drugs
Tiredness
Distractions (mobile
phones etc)
Increased Speed
Factors affecting
braking distance
Weather conditions (icy
/ wet roads)
Poor road conditions
Poor brake conditions
Increased Speed
9. Calculation of work done
• The force from the brakes on a car convert
heat energy
kinetic energy into ___________?
• The force on a car is 12kN and it stops in 5
metres. What is the work done by the brakes?
W=Fxd
W = 12000 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?
Gradient = 8/5 1.6m/s
Is this different from the speed
between 5 and 6 seconds?
No – the gradient is the same
On the return journey the
speed isn’t constant. At what
time between 11 to 18 seconds
is the speed the least?
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/s2
• 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 GRAVITATIONAL POTENTIAL ENERGY
as they travel down a hill and gains
KINETIC ENERGY . As they apply the brakes this
energy is changes into HEAT/THERMAL ENERGY
as the bike stops.
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 04 seconds?
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 = 52 + 15 = 67m
• What distance has
been travelled from
A to C?
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.
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
• Why does a balloon that is charged up stick to a wall?
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
• What would happen if you brought 2 balloons that
are charged up in a similar way together?
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=Ixt
• 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,
• diode
• LDR,
• 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.