What does the law of conservation of momentum state?
Whenever objects interact, the total momentum before the interaction is equal to the total momentum afterwards
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What are two examples of interaction events?
Collisions and explosions
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What happens to the momentum in an explosion?
The objects move apart with equal and opposite momentum. One momentum is positive and the other negative, so the total momentum after the explosion is zero
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What is the size of the force if the impact time is short?
The force on the object is large
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How do crumple zones in cars reduce the forces acting on it?
They are designed to fold in a collision so therefore this increases the impact time and the time taken to change the momentum and this reduces the force on the car
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How do seat belts reduce the force of an impact?
By increasing the time over which the wearer's momentum changes
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How do airbags reduce the force of an impact?
By spreading the forces on the body across a larger area because if someone hits one, the momentum changes slowly so the force is less
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When is the resultant force on a car zero?
If the vehicle is travelling at a steady speed
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What two forces are equal and opposite to each other on a vehicle travelling at a steady speed?
The driving forces are equal and opposite to the resistive forces
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What are the resistive forces caused by?
Air resistance and friction
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What is the stopping distance of a vehicle?
The sum of the distance the vehicle travels during the driver's reaction time and the distance it travels under the braking force
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How can a driver's reaction time be affected?
By tiredness, drugs and alcohol
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What happens when the brakes of a vehicle are applied?
Work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increases
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How can the braking distance be increased?
Poorly maintained roads, bad weather conditions and the condition of the car
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If an object falls freely, what is the resultant force acting on it?
The force of gravity
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What happens when an object falls through fluid?
The fluid exerts a drag force on the object, resisting its motion
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The faster the object falls through a fluid...?
The greater the frictional force which acts on it
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Other cards in this set
Card 2
Front
What does the momentum of an object depend on?
Back
Its mass and velocity
Card 3
Front
What does the law of conservation of momentum state?
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