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10 Cards in this Set
- Front
- Back
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What is the formula for momentum?
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Momentum = mass x velocity
kg m/s |
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What type of quantity is momentum?
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A vector - it has size and direction
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What does the conservation of momentum mean?
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Momentum before = momentum after
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Answer the question in diagram
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positive to the right (momentum = mass x velocity)
Ed = 80 x 2 = 160 kg m/s Sue = 60 x 1.5 = - 90 kg m/s 160 + -90 = 70 kg m/s velocity = momentum / mass 0.5 m/s to right = 70 / 140 (combined) |
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answer question in picture
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Total momentum before firing = 0
bullet = 0.01 x 150 = 1.5 gun = 1 x ? = -1.5 (1.5 of bullet + velocity of gun = 0 so gun must be -1.5 m/s) so velocity of gun = 1.5 / 1 = 1.5 m/s (recoil) |
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In gun example which of Newton's laws is relevant
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3rd law. gun pushes on bullet and bullet pushes back. size of force is same each way but mass of bullet and mass of gun very different so lower acceleration for gun due to larger mass (a = f / m)
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What cause changes in momentum
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Forces
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What is the formula for changes in momentum by force?
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force (N) = change in momentum (kg m/s ) / time taken for change (s)
F = (mv - mu)/ t |
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What happens in a car crash
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The change in momentum happens very quickly so big force on body
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How can you lower this force in cars??
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design cars to slow down over longer time using crumple zones. Longer it takes for car to slow down the lower the force.
Seatbelts also stretch slightly + air bags slow you down in car cabin |
