Text of AQA P2 Physics Booster 2012 Specification E Ralls
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AQA P2 Physics Booster 2012 Specification E Ralls
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Remember your units: Weight = newtons (N) Acceleration = m/s 2 Work done = joules (J)
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P2.1: Motion
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Speed = Distance Time This will not be on your data sheet
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Distance time graphs
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Speed vs. Velocity Speed is simply how fast you are travelling Velocity is speed in a given direction This car is travelling at a speed of 20m/s This car is travelling at a velocity of 20m/s east
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Velocity-time graphs 80 60 40 20 0 10 20 30 40 50 Velocity m/s Time (s) accelerating constant speed/velocity accelerating decelerating
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Acceleration vs. Deceleration Remember, if you are asked to work out the deceleration of an object, you use the same equation as you would to work out acceleration.
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P2.2: Forces
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Newton said: Objects continue to move in a state of constant velocity unless acted upon by an external net force. 1 ST LAW.
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Newton Astronauts need to beware!
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Newton also said: Every action has an equal and opposite reaction. - His 3rd law. Which explains why guns recoil and how rocket engines work.
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Another example of the third law; this time to stop the astronaut moving.
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Resultant Force When the resultant force on an object is not zero, movement depends on the size and direction of the resultant force.
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Resultant Force 60N 20N 40N
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Acceleration The acceleration of an object depends on the size of the resultant force. If the resultant force is zero the object will remain motionless or continue at a constant speed. Wind 2N Engine 4N Air resistance 3N Resultant Force 3N
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Braking Force The braking force needed to stop a vehicle is dependant on: The velocity of the vehicle when the brakes are first applied. The mass of the vehicle.
Factors Affecting Stopping Distance Tiredness, alcohol and drugs The speed that the vehicle is travelling Adverse road conditions Poorly maintained vehicle
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Weight and Mass Mass = the quantity of matter in an object Weight = the force of gravity on an object The gravitational field strength of Earth is about 10N/kg
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Weight and Mass
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Air Resistance
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Elastic Potential Energy An elastic object such as a spring stores elastic potential energy when stretched or squashed. Work is done on an elastic object when its shape changes and it stores elastic potential energy. Energy transferred by a force
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Hookes Law The extension of an elastic object is directly proportional to the force applied to it Increase in length
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P2.3: Work, Energy and Momentum
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Energy and Work When an object is moved by a force we say work is done on the object by the force. The force transfers energy to the object.
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Gravitational Potential Energy Transfers Energy stored in an object because of its position in the Earths gravitational field. The equation: change of GPE = weight x change in height joules, J newtons, N metres, m
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change of GPE = weight x change in height joules, J newtons, N metres, m
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You wont always be given a weight. Sometimes you will need to use this equation: joules, J kilograms, kg newtons per kilogram, N/kg metres, m
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Kinetic Energy
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Kinetic energy 1.If an object of mass 15kg is travelling at 5m/s, how much kinetic energy does it have? 2.A car is travelling at 30m/s and has kinetic energy of 450kJ, what is its mass? 3. A tennis ball has a mass of 0.06kg and has kinetic energy of 2.94kJ when served, what is its speed? x 15 x 25 = 187.5J m=2xKE/v 2 =2x450000/900=1000kg v= (2KE/m) = (5.88/0.6)=3.13m/s
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Momentum
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Conservation of Momentum So long as no external forces are acting on the objects involved, the total momentum stays the same in explosions and collisions.
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Conservation of momentum question Two trolleys collide and stick together. From the data below, calculate the velocity of the trolleys after the collision. trolley Atrolley B mass = 3 kgmass = 5 kg velocity = 8 m/svelocity = -4 m/s momentum = 24 kg m/s (3 x 8)momentum = -20 kg m/s (5 x -4) total momentum before collision = 4 kg m/s (24 + -20) mass after collision = 8 kg (3 + 5) momentum after collision = 4 kg m/s velocity after collision = momentum / mass = 0.5 m/s
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Investigating momentum
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Try these.. A trolley of mass 4kg moving at 10 m/s collides with a 2 kg trolley moving in the same direction at a velocity of 4m/s. they separate after the collision and the 4 kg trolley slows to 7m/s. What is the final speed of the other trolley? (hint draw diagrams of momentum before and after) a trolleyA of mass 1kg is travelling at 2m/s towards another trolleyB of mass 4kg which is travelling towards it at a velocity of 3m/s. On collision they stick together. What is their final combined velocity and in which direction do they travel together? (care with negatives) 10m/s 2m/s to the left
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Explosions and Momentum (mass of A x velocity of A) = - (mass of B x velocity of B)
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Changing Momentum Cars have crumple zones to increase impact time on collision. If you increase the impact time, it will decrease the impact force.
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P2.4: Current Electricity
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Van de Graaff generator
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When you rub two different insulated materials against each other they become electrically charged. This only works for insulated objects. Charging by Friction
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Two charged rods of different materials will attract each other if they have a different charge. Two rods made of the same material will repel each other due to having the same charge. Like charges repel: unlike charges attract
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Circuit Symbols V Battery Cell Fuse Resistor LDR Voltmeter Ammeter Variable resistor Diode Switch (open) Bulb (lamp) A
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Resistance is measured in ohms ()
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Ohms Law The current flowing through a resistor at a constant temperature is directly proportional to the voltage across the resistor. So If you double the voltage, the current also doubles.
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Ohmic resistor Filament lamp Diode The filament lamp does not follow Ohms Law. Its resistance increases as the temperature of its filament increases. The diode has a very high resistance in one direction. This means that current can only flow in the other direction.
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Series Circuits The same current passes through components in series with each other If the current through the lamps is 0.12A, what is the current through the cell? 0.12A
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Series Circuits The total potential difference of the voltage supply in a series circuit is shared between the components. If the potential difference of the cell is 1.2V and the potential difference of across one lamp is 0.8V, what is the potential difference across the other lamp? 0.4V 1.2V 0.8V 0.4V
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Series Circuits The total resistance of components in series is equal to the sum of their separate resistances. What is the total resistance if one lamp in series has a resistance of 2 and the other has a resistance of 3 ? 55 22 33
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Parallel Circuits The total current through the whole circuit is the sum of the currents through the separate components. A1A1 If ammeter A 1 reads 0.4A and A 2 reads 0.1A, what would A 3 read? 0.3A A2A2 A3A3 0.4A 0.1A 0.3A
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Parallel Circuits For components in parallel, the potential difference across each component is the same. If the potential difference of the cell is 6V, the potential difference across each lamp will also be 6V. 6V
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P2.5: Mains Electricity
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Direct current The battery in a torch uses direct current. This means it moves in one direction only.
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Direct Current
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Alternating Current Mains electricity uses an alternating current. This means that the current repeatedly reverses direction. The UK mains supply being about 230 V. It has a frequency of 50 Hz (50 hertz), which means it changes direction, and back agai
