Momentum and impulses

6.1

Standard

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HS-PS2-2. Use mathematical representations to support the claim that the total momentum of a system of objects is conserved when there is no net force on the system.

Learning objectives

I can use mathematical representation to Identify examples of change in the momentum of an object.

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I can explore the law of conservation of momentum and uses this law to predict the final velocity of an object after a collision.

Success criteria

• Calculate the momentum of the object
• Link the force done with the momentum
• Compute the impulse of an object
• Experiment the conservation of momentum
• Differentiate between elastic and inelastic collision
• Find the final velocity after the collision
• predict the final velocities of objects after collisions.

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New Vocabulary

impulse

momentum

Conservation of momentum

closed system

isolated system

Starter

https://www.youtube.com/watch?v=0zxTIn67q3Y&t=2s

Impulse-Momentum Theorem

• The impulse on an object is the product of the average force on the object and the time interval during which it acts.
• Impulse is measured in newton-seconds.
• The product of the object’s mass and the object’s velocity is the momentum of the object.

Momentum

p = mv

• Momentum is a vector quantity.
• Momentum is measured in kg·m/s.

Impulse-Momentum Theorem

• The impulse-momentum theorem states that the impulse on an object is equal to the change in its momentum.

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Impulse-Momentum Theorem

FΔt = p_f − p_i

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Real-life example

• https://www.youtube.com/watch?v=Y8Ij9xboreA

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• How the dinosaurs extinct ?

Starter

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explain why conserved momentum is a vector quantity while conserved mass and conserved energy is a scalar quantities.

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Search about

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The difference between elastic and inelastic collisions

Review Vocabulary

momentum: the product of an object’s mass and the object’s velocity; measured in kg•m/s

Momentum in a Closed, Isolated System

• A system which does not gain or lose mass is said to be a closed system.
• When the net external force on a closed system is zero, the system is described as an isolated system.

Momentum in a Closed, Isolated System

• The law of conservation of momentum states that the momentum of any closed, isolated system does not change.

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Law of Conservation of Momentum

p_f = p_i

A 76 kg boater, initially at rest in a

stationary 45 kg boat, steps out of the boat and onto the dock.

If the boater moves out of the boat with a velocity of 2.5 m/s to

the right, what is the final velocity of the boat?

Practice

Practice ( Answer)

Class work

1. A 63.0 kg astronaut is on a space walk when the tether line to the shuttle breaks.

The astronaut is able to throw a spare 10.0 kg oxygen tank in a direction away from

the shuttle with a speed of 12.0 m/s, propelling the astronaut back to the shuttle.

Assuming that the astronaut starts from rest with respect to the shuttle, find the

astronaut’s final speed with respect to the shuttle after the tank is thrown.

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2. An 85.0 kg fisherman jumps from a dock into a 135.0 kg rowboat at rest on the west

side of the dock. If the velocity of the fisherman is 4.30 m/s to the west as he leaves

the dock, what is the final velocity of the fisherman and the boat?

  1.  Here's what you know, astronaut’s

m = 63.0 kg,

tanks  = 10.0 kg,

tank's v = 12.0 m/s. 

Use the formula mv = mv. 

Plug in (10.0 kg)

        (12 m/s)   = (63.0 kg)(v).  astronaut's v = 1.9 m/s.

2. Here's what you know, fisherman’s

m = 85.0 kg,

boat's m = 135.0 kg,

fisherman's v = 4.30 m/s. 

 Use the formula mv = mv.  

Plug in (85.0 kg)(4.30 m/s) = (85.0 kg + 135.0 kg)(v).  v = 1.66 m/s.

Class work / Answers