Physics Unit 2 Revision

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What's the difference between speed and velocity?
Speed is how fast you are going no matter what direction you're going but velocity matters on the direction you're going.
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Write down the formula for acceleration.
acceleration = change in velocity/ time taken
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What's the acceleration of an object that starts off rest and reaches a speed of 14m/s in 0.4 seconds?
(14-0)/0.4=35m/s²
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Explain how to find speed from a velocity-time graph.
Read the value off the velocity axis.
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Explain how to find distance from a velocity-time graph.
Equal to the area under the graph.
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Explain how to find acceleration from a velocity-time graph.
Acceleration = gradient.
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Explain the difference between mass and weight.
Mass is the amount of stuff in an object and stays the same where ever you are. Weight is caused by the pull of gravity and changes where you are.
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Explain what is meant by a "resultant force."
The overall force on a point or object.
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If an object has zero resultant force on it, can it be moving?
Yes, because if there is no resultant force on a moving object then it will move at a steady speed.
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If an object has zero resultant force on it, can it be accelerating?
No, you get only get a zero resultant force if it is moving at a steady speed.
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Write down the formula linking resultant force and acceleration.
F=ma or a = F/m
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A resultant force of 30N pushes a trolley of mass 4kg. What will its acceleration be?
a = F/m. 30/4 = 7.5m/s²
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A man pushes a tree with a force of 120N. What is the size of the reaction force that the man feels pushing back at him?
120N
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What is "terminal velocity"?
The maxium speed of an object.
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What are the two different parts of the overall stopping distance of a car?
Thinking distance and Braking distance.
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Write down the formula for work done.
Work done = force x distance.
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A dog drags a branch 12m over the next door neighbour's front lawn, pulling with a force of 535N. How much work is done?
W = 535 x 12 = 6420J
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A 4kg cheese is taken 30m up a hill before being rolled back down again. If g=10N/kg, how much gravitational potential energy does the cheese have at the top of the hill?
Eₚ = m x g x h = 4 x 10 x 30 = 1200
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What's the formula for kinetic energy?
kinetic energy = 1/2 x mass x speed²
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Find the kinetic energy of a 78kg object moving at 23m/s²
1/2 x 78 x 23² = 20631J
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A car of mass 1000kg is travelling at a velocity of 2m/s when a sheep runs out 5m in front. If the driver immediately applies the maximum braking force of 395N, can he avoid hitting it?
Eₖ transferred = Work done by brakes. 1/2 x m x v² = F x d = 1/2 x 1000 x 4 = 395 x d. d = 2000/395 = 5.1m. No he can't avoid the sheep.
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If the total momentum of a system before a collision is zero, what is the total momentum of the system after the collision?
Zero because momentum before = momentum after.
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Explain how a) seat belts, b) crumple zones, c) side impact bars and d) air bags are useful in a crash.
a) They stretch increasing the time taken for the wearer to stop, reducing the force acting on the chest b) They Increase the impact time, decreasing the force. c) Help direct kinetic energy away from the passengersto other areas.
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What is the advantage of using regenerative braking systems?
They store the energy of braking rather than wasting it.
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What causes the build up of static electricity?
Friction
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Which particles move when static builds up?
Electrons, only negative charges move.
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True or false: the greater the resistance of a component the smaller the current that flows through it?
True.
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What's the formula for total charge in a circuit?
Current = Charge/time
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240C of charge is carried through a wire in a circuit in one minute. How much current has flowed through the wire?
C = 240/60 = 4A
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Explain how resistance of a component changes with its temperature in terms of ions and electrons.
An electrical charge flows through resistor some of electrical energy is transferred to heat energy and it gets how. it causes ions in conductor to vibrate more. Making difficult for charged electrons to move. Current can't flow resistance increases.
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What potential difference is required to push 2A of current through a 0.6 resistor?
P.D = 2 x 0.6 = 1.2V
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Describe how the resistance of an LDR varies with light intensity. Give an application.
In bright light the resistance drops. In darkness the resistance is highest. Automatic Night Lights, Outdoor Lighting, Burgular Detectors.
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An AC supply of electricity has a time period of 0.08s. What is its frequency?
f = 1/t s0 f = 1/0.08 = 12.5 Hz
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Name the three wires in a three core cable.
Neutral, Earth, Live Wires.
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Explain fully how a fuse and earth wire work together.
Fault allows live to touch metal case. Big current flows out through earth. Big current surges to earth. Big surge in current blows fuse which isolates the appliance from the live.
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How does an RCCB stop you from getting electrocuted?
If someone touches the live wire a small but deadly current will flow through them to the earth. The current will be different in the live and neutral wire which the RCCB detects and quickly cuts off the power stopping the current flowing.
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Which uses more energy, a 45W pair of hair straighteners used for 5 minutes a 105W hairdryer used for 2 minutes?
E = P x t Hair Straighteners: E = 13500J Hair dryer: E = 12 600J. Hair straighteners use more energy.
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Find the appropriate fuse (3A, 5A, or 13A) for a a) toaster rated 230V, 1100W b) an electric heater rated at 230V, 2000W
P = I x V, I = P/V a) I = 1100/230 = 4.8A Use a 5A fuse. b) I = 2000/230=8.7A so use a 13 A fuse.
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Calculate the energy transformed by a torch using a 6V battery when 530C of charge pass through.
E = Q x V, E = 530 x 6 = 3180J
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Explain how the experiments of Rutherford and Marsden led to the nuclear model of the atom.
Fired a beam of alpha particles at gold foil. Expected the positively charged alpha particles to be slightly deflected by electrons in the plum pudding model. Most of them went straight through but the odd one came back.
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State the relative mass and charge of the three basic subatomic particles.
Proton: Mass is 1, Charge is +1. Neutron: Mass: 1 Charge: 0. Electron: Mass 1/2000 Charge: -1
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True or false: radioactive decay can be triggered by certain chemical reactions?
False, radioactive decay is totally random and there is nothing you can do about it.
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What type of subatomic particle is a beta particle?
A fast moving electron.
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List two places where background radiation is increased and explain why.
Underground, in mines, increases because of th rocks around. At high altitudes, because of more exposure to cosmic rays.
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Name three occupations that have an increased risk of exposure to radiation.
Miners, Radiographers, Commercial pilots, Uranium miners, Nuclear industry workers.
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What is the definition of half life?
Half life is the AVERAGE TIME it takes for the NUMBER OF NUCLEI in a RADIOACTIVE ISOTOPE SAMPLE to HALVE.
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Give an example of how gamma radiation can be used in medicine.
Sterilisation of surgical instruments, they can be exposed to a high dose of gamma rays which will kill all microbes and won't melt any plastic instruments.
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Which is the most dangerous form of radiation if you eat it? Why?
Alpha sources because they do all their damage in a localised area. Beta and gamma sources on the other hand mostly pass straight out without doing much damage.
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Explain how the chain reaction in fission works.
A slow moving neutron must be absorbed into an uranium atom. This addition makes it unstable causing it to split. Each time it splits it gives out 2/3 neutrons, which might hit another uranium atom which splits, thus carrying on the chain reaction.
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What is the main environmental problem associated with nuclear power?
Nuclear power carries the risk of radiation leaks from the plant or a major disaster like Chernobyl. The radiation harms local wildlife, and humans themselves.
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What is nuclear fusion? Why is it difficult to construct a working fusion reactor?
Nuclear fusion is the joining of small atomic muclei. It is difficult to construct a fusion reactor because you need an extremely strong magnetic field to hold the hydrogen at the right pressure and temperature - ~10,000,000.
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Other cards in this set

Card 2

Front

Write down the formula for acceleration.

Back

acceleration = change in velocity/ time taken

Card 3

Front

What's the acceleration of an object that starts off rest and reaches a speed of 14m/s in 0.4 seconds?

Back

Preview of the front of card 3

Card 4

Front

Explain how to find speed from a velocity-time graph.

Back

Preview of the front of card 4

Card 5

Front

Explain how to find distance from a velocity-time graph.

Back

Preview of the front of card 5
View more cards

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