Momentum, Impulse, Collisions, and Conservation of Angular Momentum

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Momentum, Impulse, Collisions, and Conservation
of Angular Momentum

• Clicker Quiz

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Momentum is

1. An objects speed and direction
2. The inertia of an object
3. An objects inertia in motion
4. The force behind an accelerating object
5. Chuck Norris middle name

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Impulse is

1. a force that is applied at a random time.
2. a force that is applied very suddenly.
3. the area under the curve in a force-versus-time
   graph.
4. the time interval that a force lasts.

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Impulse is

1. a force that is applied at a random time.
2. a force that is applied very suddenly.
3. the area under the curve in a force-versus-time
   graph.
4. the time interval that a force lasts.

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Identify the correct relationship between
Momentum and velocity

1. p m a
2. p m v
3. p m / v
4. p F / v
5. p F v cos ?

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Identify the correct relationship between
Momentum and velocity

1. F m a - Newtons 2nd Law of motion
2. p m v - correct!
3. p m / v - no meaning
4. p F / v - nonsense
5. P F v cos ? - Power

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Identify the correct relationship between Impulse
and force

1. J F / t
2. J F t
3. J F d cos ?
4. J F / m
5. J F v cos ?

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Identify the correct relationship between Impulse
and force

• J F / t - no meaning
• J F t - correct!
• W F d cos ?
• a F / m - from Newtons 2nd Law (F ma)
• P F v cos ?

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When is momentum conserved during an interaction
between 2 or more objects?

1. When the objects are part of an isolated system
2. When there is no friction involved
3. When there is no net external forces acting on
   the objects
4. All of the above

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When is momentum conserved during an interaction
between 2 or more objects?

1. When the objects are part of an isolated system
2. When there is no friction involved
3. When there is no net external forces acting on
   the objects
4. All of the above - isolated means there are
   no outside forces affecting the system. Friction
   is considered an external, or outside, force.

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Why study momentum?

1. It helps us describe accelerating systems
2. It helps us easily describe complex motions of an
   object moving from one height to another under
   the acceleration of gravity (like a rollercoaster
   car)
3. It allows us to describe the speeds of two
   objects before or after they interact with each
   other
4. It allows us to describe the transfer of inertia
   from one object to another
5. Both 3 and 4

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Why study momentum?

1. It helps us describe accelerating systems
2. It helps us easily describe complex motions of an
   object moving from one height to another under
   the acceleration of gravity (like a rollercoaster
   car)
3. It allows us to describe the speeds of two
   objects before or after they interact with each
   other
4. It allows us to describe the transfer of inertia
   from one object to another
5. Both 3 and 4 - interacting could be an
   isolated collision or explosion. When 2 objects
   collide in an isolated system, their moving
   inertia (momentum) is transferred from one to the
   other.

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A perfectly elastic collision is a collision

1. between two springs.
2. that conserves potential energy.
3. that conserves thermal energy.
4. that conserves kinetic energy.
5. All of B, C, and D.

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A perfectly elastic collision is a collision

1. between two springs.
2. that conserves potential energy.
3. that conserves thermal energy.
4. that conserves kinetic energy.
5. All of B, C, and D.

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• In an inelastic collision,
• impulse is conserved.
• momentum is conserved.
• force is conserved.
• energy is conserved.
• elasticity is conserved.

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• In an inelastic collision,
• impulse is conserved.
• momentum is conserved.
• force is conserved.
• energy is conserved.
• elasticity is conserved.

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Two objects collide and bounce off each other so
that they move in opposite directions with no
loss of speed. With this information, what can
you say for certain about this event?

1. It is an inelastic collision
2. It is an elastic collision
3. Momentum is conserved
4. Kinetic energy is conserved

1. I and III only
2. II and III only
3. II, III and IV
4. I, III and IV

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Two objects collide and bounce off each other so
that they move in opposite directions with no
loss of speed. With this information, what can
you say for certain about this event?

1. It is an inelastic collision
2. It is an elastic collision
3. Momentum is conserved
4. Kinetic energy is conserved

1. I and III only
2. II and III only
3. II, III and IV Momentum is conserved in all
   collisions (w/o friction). Perfect Elastic
   collisions have no loss of speed, so KE is
   conserved too!
4. I, III and IV

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Two objects collide and stick together. With no
friction and no loss of mass, what can you say
for certain about this event?

1. It is an inelastic collision
2. It is an elastic collision
3. Momentum is conserved
4. Kinetic energy is conserved

1. I and III only
2. II and III only
3. II, III and IV
4. I, III and IV

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Two objects collide and stick together. With no
friction and no loss of mass, what can you say
for certain about this event?

1. It is an inelastic collision
2. It is an elastic collision
3. Momentum is conserved
4. Kinetic energy is conserved

1. I and III only - Momentum is conserved in all
   frictionless collisions. Inelastic collisions
   result in greater mass moving at slower speed, so
   KE is not conserved.
2. II and III only
3. II, III and IV
4. I, III and IV

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The carts change of momentum is NOTE Left is
the negative direction

1. 30 kg m/s.
2. 20 kg m/s.
3. 10 kg m/s.
4. 10 kg m/s.
5. 30 kg m/s.

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The carts change of momentum is

1. 30 kg m/s.
2. 20 kg m/s.
3. 10 kg m/s.
4. 10 kg m/s.
5. 30 kg m/s.

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A 10 g rubber ball and a 10 g clay ball are
thrown at a wall with equal speeds. The rubber
ball bounces, the clay ball sticks. Which ball
exerts a larger impulse on the wall?

1. The clay ball exerts a larger impulse because it
   sticks.
2. The rubber ball exerts a larger impulse because
   it bounces.
3. They exert equal impulses because they have equal
   momenta.
4. Neither exerts an impulse on the wall because the
   wall doesnt move.

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A 10 g rubber ball and a 10 g clay ball are
thrown at a wall with equal speeds. The rubber
ball bounces, the clay ball sticks. Which ball
exerts a larger impulse on the wall?

• The clay ball exerts a larger impulse because it
  sticks.
• The rubber ball exerts a larger impulse because
  it bounces.
• Bouncing completely changes the balls momentum
  from one direction to zero to the opposite
  direction in a split second. Stopping merely
  changes the momentum to zero.
• They exert equal impulses because they have equal
  momenta.
• Neither exerts an impulse on the wall because the
  wall doesnt move.

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Objects A and C are made of different materials,
with different springiness, but they have the
same mass and are initially at rest. When the
ball (B) collides with object A, the ball ends
up at rest. When the ball is thrown with the same
speed and collides with object C, the ball
rebounds to the left. Compare the velocities of A
and C after the collisions. Is vA greater than,
equal to, or less than vC?

1. vA gt vC
2. vA vC
3. vA lt vC

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Objects A and C are made of different materials,
with different springiness, but they have the
same mass and are initially at rest. When ball B
collides with object A, the ball ends up at rest.
When ball B is thrown with the same speed and
collides with object C, the ball rebounds to the
left. Compare the velocities of A and C after the
collisions. Is vA greater than, equal to, or less
than vC?

• vA gt vC
• vA vC
• vA lt vC
• Bouncing produces greater
• Change in momentum,
• a.k.a. greater impulse.
• And because J F t,
• Greater impulse means
• Greater force, which means
• C gets more acceleration
• And therefore a greater final
• velocity.

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An explosion in a rigid pipe shoots out three
pieces. A 6 g piece comes out the right end. A 4
g piece comes out the left end with twice the
speed of the 6 g piece. From which end does the
third piece emerge?

1. Left end
2. Right end

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An explosion in a rigid pipe shoots out three
pieces. A 6 g piece comes out the right end. A 4
g piece comes out the left end with twice the
speed of the 6 g piece. From which end does the
third piece emerge?

1. Left end
2. Right end

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The two particles are both moving to the right.
Particle 1 catches up with particle 2 and
collides with it. The particles stick together
and continue on with velocity vf . Which of these
statements is true?

1. vf is greater than v1.
2. vf v1.
3. vf is less than v2.
4. vf v2.
5. vf is greater than v2, but less than v1.

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The two particles are both moving to the right.
Particle 1 catches up with particle 2 and
collides with it. The particles stick together
and continue on with velocity vf. Which of these
statements is true?

1. vf is greater than v1.
2. vf v1.
3. vf is less than v2.
4. vf v2.
5. vf is greater than v2, but less than v1.

31
A dry ice (solid carbon dioxide) puck revolves in
a circle on the end of a lightweight rigid rod
that turns on frictionless bearings. A cushion of
CO2 gas allows the puck to glide across the
surface without friction. As the puck sublimates
(changes from a solid to a gas), its speed

1. increases.
2. decreases.
3. stays the same.

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A dry ice (solid carbon dioxide) puck revolves in
a circle on the end of a lightweight rigid rod
that turns on frictionless bearings. A cushion of
CO2 gas allows the puck to glide across the
surface without friction. As the puck sublimates
(changes from a solid to a gas), its speed

1. increases. Without friction p is conserved
   mivi mfvf As mass is lost from the puck, the
   velocity will increase
2. decreases.
3. stays the same.

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Two buckets spin around in a horizontal circle on
frictionless bearings. Suddenly, it starts to
rain. As a result,

1. The buckets slow down because the angular
   momentum of the bucket rain system is
   conserved.
2. The buckets continue to rotate at constant
   angular velocity because the rain is falling
   vertically while the buckets move in a horizontal
   plane.
3. The buckets continue to rotate at constant
   angular velocity because the total mechanical
   energy of the bucket rain system is conserved.
4. The buckets speed up because the potential energy
   of the rain is transformed into kinetic energy.
5. None of the above.

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Two buckets spin around in a horizontal circle on
frictionless bearings. Suddenly, it starts to
rain. As a result,

• The buckets slow down because the angular
  momentum of the bucket rain system is
  conserved.
• The buckets continue to rotate at constant
  angular velocity because the rain is falling
  vertically while the buckets move in a horizontal
  plane.
• The buckets continue to rotate at constant
  angular velocity because the total mechanical
  energy of the bucket rain system is conserved.
• The buckets speed up because the potential energy
  of the rain is transformed into kinetic energy.
• None of the above.
• This is like the dry ice puck question, except
  mass is added instead of lost, so the velocity of
  the system decreases so that mivi mfvf