# Physics Unit 2.2 The kinetic energy of objects speeding up or slowing down

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When an object speeds up or slows down, its kinetic energy increases or decreases. The forces which cause the change in speed do so by doing work. The momentum of an object is the product of the object's mass and velocity.
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What happens when a force causes an object to move through a distance?
Work is done.
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Describe regenerative brakes.
When the car brakes, the kinetic energy of the car is converted to electrical energy, and stored in a battery.
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Give the advantages of regenerative braking.
Less energy is wasted than conventional brakes. Less petrol is needed, so lowers CO2 emissions. Useful in city environments, where there is constant braking.
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Give the disadvantages of regenerative braking.
Cost more than regular brakes. Not useful in motorway driving.
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What is power?
Work done or energy transferred in a given time.
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What is gravitational potential energy?
Is the energy that an object has by virtue of its position in a gravitational field.
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What does the kinetic energy of an object depend on?
It's mass, and speed.
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What is momentum?
Property of moving objects.
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In a closed system, total momentum before an event is equal to ...
the total momentum after the event. This is called conservation of momentum.
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Describe forces in a rocket, or jet engine.
As the fuel burns, exhaust gases are produced. The rocket engine pushes these gases out backwards. The gases push the space shuttle forwards, with the same size force in the opposite direction.
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## Other cards in this set

### Card 2

#### Front

What happens when a force causes an object to move through a distance?

Work is done.

### Card 3

#### Front

Describe regenerative brakes.

### Card 4

#### Front

Give the advantages of regenerative braking.

### Card 5

#### Front

Give the disadvantages of regenerative braking.