A mass falling while attached to a massive pulley.
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Composition Setup
A bucket for collecting water from a well is suspended by a rope which is wound around a pulley. The empty bucket has a mass of 2.0 kg, and the pulley is essentially a uniform cylinder of mass 3.0 kg on a frictionless axle. Suppose a person drops the bucket (from rest) into the well.
We will consider two different methods to obtain the solution.
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littledeck
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label
Method 1
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sysa1
Systems:
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sysa1
The pulley and the bucket are treated as separate objects. The bucket can be treated as a , but the pulley must be treated as a .
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inta1
Interactions:
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inta1
The pulley and the bucket are each subject to external influences from the rope and from . The pulley is also subject to a from the axle.
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moda1
Model:
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moda1
and
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appa1
Approach:
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appa1
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inta2
Interactions:
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inta2
The system is subject to external forces from the earth acting on the bucket and the pulley (gravity) and from the axle acting on the pulley (contact force). If we choose the axis of rotation to coincide with the axle of the pulley, then the axle's force and gravity acting on the pulley each produce no torque. We need only consider the effects of gravity acting on the bucket.
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moda2
Model:
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moda2
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appa2
Approach:
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appa2
Card
Method 2
Method 2
Deck of Cards
littledeck
littledeck
Card
Part A
Part A
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label
Part B
Part B
What is the bucket's speed after falling 5.0 m down the well?
Solution
Again, we will use two methods.
Deck of Cards
id
littledeck2
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label
Method 1
Method 1
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id
sysb1
System:
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sysb1
Bucket as .
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intb1
Interactins:
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intb1
External influences from the earth (gravity) and the rope (tension).
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modb1
Model:
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modb1
One-Dimensional Motion with Constant Acceleration.
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appb1
Approach:
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appb1
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Method1
Method1
Card
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Method 2
Method 2
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id
sysb2
System:
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sysb2
Treat the bucket, pulley and the earth as a single system.
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id
intb2
Interactions:
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intb2
Internal interactions of gravity (conservative) and tension from the rope (non-conservative) plus an external influence from the normal force on the pulley (non-conservative).
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id
modb2
Model:
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id
modb2
.
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id
appb2
Approach:
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id
appb2
Card
Method 2
Method 2
Deck of Cards
littledeck2
littledeck2
Card
Part B
Part B
Deck of Cards
bigdeck
bigdeck
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