AQA P2 2.2 The kinetic energy of objects speeding up or slowing down

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  • Created by: Rchilds
  • Created on: 01-06-17 17:45
What does work done mean?
It is equal to the energy transferred by a force when it moves an object over a distance
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What is the unit of energy?
Joule
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What is the unit of work?
Joule (because it is equal to energy transferred)
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When you lift an object, what are you working against?
gravity (the weight of the object)
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When moving an object sideways, what are you working against?
Friction
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What is power?
the work done or energy transferred in a given time.
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What is the unit of power?
Watt
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What is gravitational potential energy?
the energy that an object has by virtue of its position in a gravitational field. It depends on how high the object is, it's mass and how strong gravity is (gravitational field strength)
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What is gravitational potential energy measured in?
Joules (because it is an energy)
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What is kinetic energy?
The energy an object has because it is moving, it depends on mass and speed.
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What is kinetic energy measured in?
Joules (because it is an energy)
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What is momentum?
A property of moving objects = mass x velocity
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What are the units for momentum?
kgm/s
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What does conservation of momentum mean?
In a closed system the total momentum before an event is equal to the total momentum after the event
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How do you solve a momentum problem? (2 cards)
1) draw a diagram of before the collision and after the collision 2) summarise all the mass and velocity information given in the question 3) choose which direction is a positive velocity and negative and put the + and - before your velocities...
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momentum problems continued...
4) calculate the momentums of all the objects individually, leave any unknown numbers as symbols. 5) add together the momentums before the collision 6) add together the momentums after the collision 7) put steps 5 and 6 equal to each other and solve
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Momentum problems for explosions? Explosions are any situation when neither object is moving then they push apart e.g. skaters, bullet and gun etc.
The momentum before = 0 as nothing is moving, the momentum of each object afterwards must be equal and in opposite directions so they cancel out each other's momentum back to zero (as total momentum must be conserved).
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How do seatbelts help protect a person in a vehicle?
They stretch slightly, increasing the time taken to stop. So for the same momentum change (as momentum goes to zero) this reduces the deceleration so the impact force on the person is smaller reducing the risk of injury.
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How do crumple zones at the front of a car help protect a person in a vehicle?
It crumples, increasing the time taken to stop. So for the same momentum change (as momentum goes to zero) this reduces the deceleration so the impact force on the person is smaller reducing the risk of injury.
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How do the air bags of a car help protect a person in a vehicle?
They gradually deflate, increasing the time taken for the person to stop. So for the same momentum change (as momentum goes to zero) this reduces the deceleration so the impact force on the person is smaller reducing the risk of injury.
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Other cards in this set

Card 2

Front

What is the unit of energy?

Back

Joule

Card 3

Front

What is the unit of work?

Back

Preview of the front of card 3

Card 4

Front

When you lift an object, what are you working against?

Back

Preview of the front of card 4

Card 5

Front

When moving an object sideways, what are you working against?

Back

Preview of the front of card 5
View more cards

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