Linear Momentum

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Linear Momentum
Physics Mrs. Coyle
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Linear Momentum, p

• p m v
•  
• Momentum is a vector.
• The direction of momentum is the same as the
  direction of the velocity of the object.
• Unit kg m/s or N s
• Inertia in Motion

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Question 1

• What has more momentum, a dump truck at rest or
  a pebble moving down a hill at 1m/s?

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Question 2

• How can you change the momentum of an object?

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Impulse
Change in Momentum

• Impulse ?p m ?v Ft

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Problem 1

• Starting with Newtons second law, show that for
  a constant force, ?p m ?v Ft .

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For a given change in velocity, ?p is constant
D
p F t
To reduce the force of impact, increase the time
of impact.
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Question 3

• How do you have a better chance of winning in a
  water balloon toss contest?

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Question 4

• Why does a boxer roll with the punches?

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Question 5

• Why should you follow through in a serve when
  playing tennis, or when hitting a baseball?

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Problem 2

• A ball at rest has a mass 0.5kg and
• is kicked with a force of 40N. The
• impact lasts 0.2s. Find
• The change in momentum of the ball.
• The final velocity of the ball.Answer a) 8 Ns,
  b)16m/s

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Problem 3

• A football player of mass 130kg travelling at
  12.0m/s collides with another player and comes to
  rest in 0.90s. What was the force of impact?
• Answer1,733N

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Impulse is the area under the curve in a graph of
F vs t.
F
t
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Some Engineering Applications
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Question 6

• Why are airbags used?

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M A R S E XPLORATION
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MARS LANDER AIR BAGS
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Rover Exits the Lander
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Applications in Engineering Household Items
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MILK BOTTLES
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THE EGG CARTON