P2 Physics
Additional Science
Key Recall Questions
*Cover up the answers, ask yourself a question (or get your partner to ask you), if you get it right then tick the chart, wrong put a cross. Keep practising until all columns are ticked!
P2.1 Forces and their effects_1
Key Recall Question / Answer1. How are forces represented? / By an arrow, ideally from where the force originates
2. What is a resultant force? / A single force which replaces a number of forces all acting at a particular point. The resultant force has the same effect on the motion as all the forces acting together.
3. What will happen if the resultant force acting on a stationary object is zero? / The object will stay stationary.
4. What will happen if the resultant force acting on a stationary object is not zero? / The object will accelerate in the direction of the resultant force.
5. What will happen if the resultant force acting on a moving object is zero? / The object will move at the same speed and in the same direction.
6. What will happen if the resultant force acting on a moving object is not zero? / The object will accelerate in the direction of the resultant force.
7. What is the unit for force? / Newtons (N)
8. How are force, mass and acceleration linked? / Force = mass x acceleration
F(N) = m (kg) x (m/s2)
9. What are the units of mass? / Kilograms (kg), grams (g) or sometimes tonnes (1000kg)
10. What is the unit of acceleration? / Metres per second squared (m/s2)
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P2.1 Forces and their effects_2
Key Recall Question / Answer1. What does the gradient of a distance-time graph represent? / Constant speed (velocity)
2. What are the units of speed (velocity)? / Metres per second (m/s) or kilometres per hour (km/hr). NOTE; miles per hour is not an SI unit.
3. What does a horizontal line on a distance-time graph represent? / The object is stationary.
4. How do you calculate the speed (velocity) from a distance-time graph? / Speed (velocity) is distance/time so use the axis to find the distance travelled and divide it by the time taken.
5. What is the difference between speed and velocity? / The velocity of an object is its speed in a given direction.
6. What does the gradient of a velocity-time graph represent? / Acceleration.
7. What are the units for acceleration? / metres per second squared (m/s2)
8. What does a horizontal line on a velocity-time graph represent? / The object is moving at a constant velocity.
9. How do you calculate the acceleration from a velocity-time graph? / Use a = v-u
t
Where a = acceleration (m/s2), v = final velocity (m/s), u = initial velocity (m/s) and t = time (s)
10. How do you calculate the distance from a velocity-time graph? / Work out the area underneath the graph. The answer will be in metres (m).
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P2.1 Forces and their effects_3
Key Recall Question / Answer1. What happens to the forces when a vehicle travels at a steady speed? / The resistive forces balance the driving force
2. Which force are most of the resistive forces acting on a vehicle caused by? / Air resistance.
3. How is the braking force affected by speed? / The bigger the speed the greater the braking force required to stop it in a certain distance.
4. What is ‘stopping distance’? / The distance the driver travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance).
5. What three things can a driver’s reaction time be affected by? / Tiredness, drugs and alcohol.
6. What happens to the temperature of the brakes when you apply them and why? / It increases because the work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle so the temperature of the brakes increases.
7. What can braking distance be affected by? / Poor weather (icy and wet conditions) and poor condition of the vehicle (tyres or brakes).
8. If an object moves through a fluid (liquid or gas) faster, what happens to the frictional force? / It will increase
9. Why does a falling object initially accelerate? / Due to the force of gravity
10. What will eventually happen to the resultant force of a falling object? / It will be zero
11. What is ‘terminal velocity’? / The speed (velocity) an object reaches when the resultant forces are zero. It is measured in m/s
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P2.1 Forces and their effects_4
Key Recall Question / Answer1. How do you calculate the weight of an object? / Mass(kg) x gravity (N/kg) = Weight (N)
2. What will happen to a spring when a force is applied? / It will change shape and stretch
3. What type of energy is stored in a spring when it is stretched? / Elastic potential energy
4. What is the extension for an elastic object directionally proportional to? / The force applied
5. What is the limit of proportionality? / The point at which the force applied and extension is no longer proportional
6. In F = k x e, what does e represent? / The extension in metres.
7. In F = k x e, what does k represent? / The spring constant
8. What are the units for ‘spring constant’? / Newtons per metre (N/m)
9. If a spring has a spring constant of 3 and it is extended by 0.1 m, what is the Force applied to produced this extension? / F = k x e
F = 3 x 0.1
F = 0.3 N
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P2.2 The kinetic energy of objects speeding up or slowing down_1
Key Recall Question / Answer1. What is ‘work done’? / When a Force causes an object to move through a distance. W = F (N) x d (m)
2. What is the unit for work done? / Joules (J)
3. What is transferred when work is done on an object? / Energy
4. Will the amount of work done to move an object across ice be smaller or greater than to move the same object, the same distance across grass? / It will be smaller because there are less frictional forces to counteract.
5. What is ‘Power’ and what are its units? / The work done or energy transferred in a given time.
P = E/t. The units for Power are Watts (W), Energy are joules (J) and time is seconds (s)
6. What is gravitational potential energy? / The energy that an object has due to its position in a gravitational field. Ep = m x g x h
Where Ep is the change in gravitational potential energy in joules (J), m is the mass in kilograms (kg), g is the gravitational field strength in newtons per kilogram (N/kg) and h is the change in height in metres (m)
7. What are the units for gravitational field strength (g)? / N/kg
8. If the gravitational field strength on Earth is 10 N/kg what is the weight of someone who has a mass of 70 kg? / 70 kg x 10 N/kg = 700 N
(weight = m x g)
9. If the person in question 8 stood on a stool which is 1m high, what would their gravitational potential energy be? / Ep = m x g x h
Ep = 70 x 10 x 1
Ep = 70 J
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P2.2 The kinetic energy of objects speeding up or slowing down_2
Key Recall Question / Answer1. What two factors does the kinetic energy of an object depend on? / Mass and speed. Ek = ½ x m x v2
2. How can the kinetic energy equation be rearranged to calculate speed? / V = 2 x Ek
M
3. What must an object be doing in order to have momentum? / Moving
4. What is the equation for calculating momentum? / p = m x v
p is momentum in kilogram metres per second (kg m/s), m is mass in kilograms (kg) and v is velocity in metres per second (m/s)
5. How does the momentum of an object before a collision or explosion compare to the momentum after a collision (assuming it is a closed system)? / It is equal
6. What are the units for momentum? / kg m/s
7. If an object has a momentum of 30 kg m/s and it collides into another object and sticks to it, what will the momentum of the two objects be? / 30 kg m/s
8. The mass of the two objects in question 7 is 10 kg. What will the velocity of the objects be? / v = p/m, v = 30/10 so v = 3 m/s
9. When a cannon is fired it often moves backwards. What is this backward movement called? / Recoil
10. How can the momentum of the recoil of a gun be the same as the momentum of the bullet, but the person firing the gun is not injured? / Because the mass of the bullet is much smaller than the mass of the gun. Therefore the velocity of the bullet can be much greater than the velocity of the gun, thus making the momentum of the two objects the same.
11. If two ice skaters, of mass 60 kg and 90 kg, are standing in the middle of an ice rink and they push against each other, which ice skater will move with the greatest velocity? / The 60 kg ice skater because to equal the momentum of the other ice skater (p = m x v) they must have a greater velocity.
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P2.3 Currents in electrical circuits_1
Key Recall Question / Answer1. What happens when insulating materials are rubbed against each other? / They become electrically charged.
2. What particle is rubbed off between each insulating material when they are rubbed together? / Electrons (which have negative charges)
3. How does one of the insulating materials become negatively charged? / It gains electrons (from the other insulating material)
4. How does one of the insulating materials become positively charged? / It loses electrons (to the other insulating material)
5. What happens if two electrically charged objects are brought together? / They exert a force on each other (e.g. a charged balloon near to charged hair)
6. If two electrically charged materials, which carry the same charge, are brought near to each other what will happen? / They will repel each other.
7. If two electrically charged materials, which carry different charges, are brought near to each other what will happen? / They will attract each other.
8. What sort of materials can electrical charges move through easily? / Metals (think back to chemistry and their structure to understand why)
9. What is electric current? / The flow of electric charge.
10. What does the size of electric current depend on? / The rate of flow of electric charge.
11. How can the size of current be calculated? / I = Q/t
where I is current in amperes (A), Q is the charge in coulombs (C) and t is the time in seconds (s).
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P2.3 Currents in electrical circuits_2
Key Recall Question / Answer1. What is the potential difference (voltage) between two points in an electric circuit? / The work done (energy transferred) per coulomb of charge that passes between the points.
2. How can potential difference be calculated? / V = W/Q
where V is the potential difference in volts (V), W is the work done in joules (J) and Q is the charge in coulombds (C)
3. What do these circuit symbols represent?
/
/ Open switch, closed switch, lamp and fuse
4. What do these circuit symbols represent?
/ Cell, battery, resistor and voltmeter
5. What do these circuit symbols represent? / Ammeter, light dependent resistor (LDR), variable resistor and thermistor
6. What do these circuit symbols represent? / Light emitting diode (LED), light dependent resistor (LDR) and diode.
7. What are current-potential difference graphs used for? / They show how the current through a component varies with the potential difference across it.
8. What does the current-potential difference graph for a resistor at constant temperature look like? / A straight diagonal line going through the point of origin.
9. What is the current through a resistor (at a constant temperature) directly proportional to? / Potential difference across the resistor.
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P2.3 Currents in electrical circuits_3
Key Recall Question / Answer1. How can the resistance of a component be found out? / By measuring the current through it and the potential difference across it.
2. How can current, potential difference and resistance be calculated? / V = I X R
Where V is the voltage in volts (V), I is the current in amperes (A) and R is the resistance in ohms (.
3. If a component has a resistance of 10 and a current of 2 A is passing through it, what will be the potential difference? / 20 V
4. If a component, which has a larger resistance than the component in question 3, is placed in the circuit, what will happen to the current? / It will be smaller.
5. How do you work out the potential difference of four 3 V cells connected in series? / The potential difference is the sum of the potential difference of each cell so 3 + 3 + 3 + 3 = 12 V
6. If one of the cells in question 5 was connected a different way around, what would the potential difference be? / 0 V (no current will flow)
7. When three 2 resistors are place in series, how can you calculate the total resistance? / Total resistance is the sum of the resistance in each component so 2 + 2 + 2 = 6
8. If a lamp, resistor and fuse (which all have different resistance) are connected in series, what do we know about the current in each component. / It will be the same.
9. What is the total potential difference across all of the components in question 8 if the potential difference from the power supply is 30 V? / 30 V (because the total potential difference of the supply is shared across all components in a parallel circuit)
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P2.3 Currents in electrical circuits_4
Key Recall Question / Answer1. If components are connected in a parallel circuit what do we know about the potential difference? / The potential difference across each component is the same.
2. If there is a 20 V cell and two lamps (with different resistance) connected in parallel to the cell, what would the potential difference across each lamp be? / 20 V across each lamp
3. If the current through lamp in the first branch of the circuit is 4 A and the second branch is 10 A, what is the total current in the whole circuit? / The total current in a parallel circuit is the sum of the currents through the separate components so 10 + 4 = 14 A
4. Which component does this current-potential difference graph represent and why?
/ A filament bulb because the graph shows that the resistance of the filament bulb increases as the temperature of the bulb increases.
5. Can you explain ‘resistance’? / An electric current flows when electrons move through conductors. As they move through the conductor they collide with ions, this collision between electron and ion in the conductor is what causes resistance.
6. Why does increasing the length of a wire increase resistance? / Electrons collide with ions more frequently (as there are more ions for them to collide with)
7. Why does a thin wire have a higher resistance than a thick wire? / Because there are fewer electrons to carry the current in a thin wire and these will collide with the ions.
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P2.3 Currents in electrical circuits_5
Key Recall Question / Answer1. What component does this graph represent and why?
/ A diode, because it shows current only flowing in one direction, the diode has a very high resistance in the reverse direction.
2. How do Light Emitting Diodes (LEDs) work? / They only emit light when current flows through in the forward direction.
3. Why are LEDs becoming more popular? / Because they use a much smaller current than other forms of lighting.
4. Can you give an example of how LEDs are used? / In small lights (e.g torches) and indicator lights in electrical equipment (e.g. computers and TVs)
5. How does the resistance of a light dependent resistor (LDR) vary with light intensity? / The resistance decreases as light intensity increases.
6. Can you give an example of how LDRs might be used? / To switch lights on when it starts to get dark.
7. How does the resistance of a thermistor vary as temperature increases? / The resistance decreases.
8. Can you give an example of how thermistors might be used? / In thermostats which regulate central heating and fire alarms.
9. Can you explain how a thermistor in a fire alarm might work? / As the temperature increases, the resistance in the thermistor decreases so current flows. This allows current to flow around the circuit to sound the alarm.
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P2.4 Using mains electricity safely and the power of electrical appliances_1
Key Recall Question / Answer1. What is direct current (d.c.)? / Current that always passes in the same direction.
2. What sorts of power supplies produce direct current? / Cells and batteries.
3. What is alternating current (a.c.)? / Current which is constantly changing direction.
4. What sort of power supplies produce alternating current? / Main electricity.
5. What sort of electricity is represented by this oscilloscope trace?
/ a.c.
6. If the above oscilloscope trace represents 1 second, what is the frequency of the supply? / 2 cycles per second (hertz)
7. What is the frequency and potential difference of mains electricity? / 50 hertz and 230 V (approx)
8. How are most electrical appliances connected to mains electricity? / Using cable and three pin plugs.
9. Which two wires are always found in electrical cables? / Live and neutral
10. Which third wire is often found in electrical cables? / Earth
11. Why do some wires not have an Earth wire? / Because the appliance they are attached to have plastic casing (double insulated) or the live wire cannot touch the casing. Therefore they cannot cause electric shocks.
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P2.4 Using mains electricity safely and the power of electrical appliances_2