momentum momentum is a vector quantity since velocity is a vector
TRANSCRIPT
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Momentum
Momentum is a vector quantity since velocity is a vector.
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ImpulseDefined as a force exerted during a time period
Impulse is the cause of a change in momentum.
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Elastic Cord vs a Steel Wire for same block on frictionless surface
Compare the impulse provided by both cord & wire from the time they reach their relaxed length to when the blocks stop.
Elastic
Steel
Jumping from table, mats, packaging
Both the elastic cord & steel wire are equal in length relaxed.
The blocks are given a quick, equal push, sending them sliding towards the right.
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Example
During an automobile crash test, a 1000kg car is sent towards a cement wall at a speed of 14m/s and is brought to a stop in 0.08 seconds. Determine force car exerted on the wall.
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Example2
A ball of mass 0.25kg is dropped from a height of 0.75m. The ball bounces back upwards from the floor with a speed of 1.5m/s.
a) Determine the speed the ball strikes the floor prior to bouncing back upwards.
b) Determine the impulse the ball receives from the floor.
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Bus hits bug!Who receives the greater impulse, bug or bus?
Who receives the greater change in momentum, bug or bus?
Who undergoes the greater acceleration, bug or bus?
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a) Find the magnitude of the impulse delivered to the object.
b) Determine the change in the object's momentum.
c) If the object's original velocity was -10m/s, calculate its final velocity.
d) What was the magnitude of the "average force" acting on the object during the time graphed?
Force-time graph
A varying, one-dimensional force acts on a 50kg mass as shown in the graph.
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Stick vs Bounce + demo
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Law of Conservation of Momentum
Total momentum before collision equals total momentum after collision assuming no external forces acting during collision.
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3 types of collisions3 types of collisions
• ELASTIC
• INELASTIC
• Perfectly Inelastic
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‘p’ conservation equations
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KE for collisions
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Example• Running at 2.0m/s, a 45-kg quarterback, collides with
a 90-kg tackle, who is traveling towards him at 7.0m/s. Upon colliding, the tackle continues to travel forward towards the quaterback at 1.0 m/s. Find velocity of quarterback.
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ExampleDuring target practice, a man shoots a 7-gram bullet with a horizontal velocity of 150 m/s directly at a 2-kg pumpkin sitting on a post. If the bullet embeds in the pumpkin, how fast will the pumpkin be knocked off the post?
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Example An 88kg fullback moving east with a speed
of 5.0m/s is tackled by a 97kg opponent running west at 3.0m/s. Assume the collision is inelastic.
a) Find the velocity of the two immediately after the collision.
b) Find the % of kinetic energy lost during the collision.
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Example • Jack and Leon are fishing in their boat when they
decide to jump into the water. Jack, 45-kg, jumps off the front of the boat with a speed of 2m/s. While at the exact same moment, Leon, 90-kg, jumps out of the back of the boat at a speed of 4m/s.
If the boat has a mass of 100 kg and was at rest prior to the two boys jumping off, what will be its velocity just after both boys have abandoned ship?
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Jumping upwards
What happens to the earth, technically speaking, when you jump upwards with glee cuz you can’t wait for physics class? Why?
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The recoil momentum of a gun that kicks is ____ the momentum of the bullet it fires.