# P2.3.3 Kinetic Energy + P2.3.4 Momentum + P2.3.5 Explosions + P2.3.6 Impact Forces + P2.3.7 Car safety

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• Created on: 24-04-14 22:21
What does the kinetic energy of an object depend on?
The kinetic energy of a moving object depends on its mass and its speed.
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How can we calculate the kinetic energy of an object?
Kinetic Energy (J) = 1/2 x mass (kg) x speed (m/s)
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What is elastic potential energy?
Elastic potential energy is the energy stored in an elastic object when work is done on the object to change its shape.
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What energy transfers occur when an elastic band is stretched and released?
Elastic potential energy => kinetic energy.
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How can we calculate momentum?
Momentum = mass x velocity
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What is the unit of momentum?
The unit of momentum is kgm/s.
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What happens to the the total momentum of two objects when they collide?
Momentum is conserved whenever objects interact, provided the objets are in a closed system so that no external forces act on them.
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Why does momentum have a directin as well as size?
Momentum is mass times velocity and velocity depends on direction as well as size.
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When two objects push each other apart do they move away at different speeds?
They move apart at different speeds if they have unequal masses.
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When two objects push each other apart why is their total momentum zero?
They move apart with equal and opposite momentum so their total momentum is zero.
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When vehicles collide, what does the force of the impact depend on?
When two vehicles collide the force of the impact depends on mass, the change of velocity, and the duration of the imapct.
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How does the impact force depend on the impact time?
The longer the impact is, the more the impact force is reduced.
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What can we say about the impact forces and the total momentum when two vehicles collide?
When two vehicles collide, they exert equal and opposite forces on each other and their total momentum is unchanged.
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Why do cars have crumple zones at both the front and the rear?
Cars may be hit from either the front or the rear, in either cases the crumple zone reduces the forces on the car and increases impact time.
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Why do seat belts and air bags reduce the force on people in car accidents?
Seat belts and air bags spread the force across the chest and they also increase the impact time.
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How do side impact bars and crumple zones work?
Side impact bars and crumple zone 'give way' in an impact so increasing the impact time.
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How can we work out if a car in a crash was 'speeding'?
We can use the conservation of momentum to find the speed of a car before an impact.
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## Other cards in this set

### Card 2

#### Front

How can we calculate the kinetic energy of an object?

#### Back

Kinetic Energy (J) = 1/2 x mass (kg) x speed (m/s)

### Card 3

#### Front

What is elastic potential energy?

### Card 4

#### Front

What energy transfers occur when an elastic band is stretched and released?

### Card 5

#### Front

How can we calculate momentum?