Window Washer w/ Bucket-Pulley Apparatus

[hawkeye1029]

Homework Statement

A window washer pulls herself upward using the bucket-pulley apparatus shown in the figure. The mass of the person plus the bucket is 65 kg.
a) How hard must she pull downward to raise herself slowly at constant speed?
b) If she increases this force by 10%, what will her acceleration be?

Homework Equations

F = ma

The Attempt at a Solution

This is where I got confused. I tried to get help from other websites, but their free-body diagrams had forces like normal force on the end the person was pulling on.
Would the force she needs to pull down on simply the gravitational force acting on her? Or would it be something else!
Thanks everyone :).

 

[haruspex]

Never mind about other websites, draw you own FBD.
First, decide whether you want to treat the person and the bucket as separate objects or one.
List the forces acting on each object, and their directions. Assign symbols to unknown forces as necessary.

 

[hawkeye1029]

Sorry for the late reply, I was away.
So would the FBD look something like this? (attached below) Or am I missing some forces?

 

[hawkeye1029]

Is there also a tension force on the left side?

 

[haruspex]

Sorry for the late reply, I was away.
So would the FBD look something like this? (attached below) Or am I missing some forces?

My only access is via iPad, and .docx pictures don't display properly.
You mention "pulling force". How is this different from tension?

 

[hawkeye1029]

I'm probably wrong, but tension force is upwards while the "pulling force" is downwards?

 

[haruspex]

I'm probably wrong, but tension force is upwards while the "pulling force" is downwards?

Tension is not so much a force as a pair of equal and opposite forces. (Likewise compression.) If you pull on a rope, the rope pulls on you equally. At any point along the rope, if we consider the lengths of rope each side of that point as separate bodies, each pulls on the other - that is tension.

In drawing a free body diagram for a body, you consider all the forces acting on that body. If the body is a person pulling on a rope, there is the force the rope exerts on the person, but not the force the person exerts on the rope - that force is acting on the rope, not on the person.

 

[hawkeye1029]

Ah, so the "pulling force" is actually the tension?

 

[haruspex]

Ah, so the "pulling force" is actually the tension?

Yes.

 

[hawkeye1029]

Are the two tensions the same? In other words would the tension equal the gravitational force on the window washer?

 

[haruspex]

Are the two tensions the same? In other words would the tension equal the gravitational force on the window washer?

Those are two different questions.
Let the tension have magnitude T. List the external forces acting on the washer+bucket system.

 

[hawkeye1029]

Um tension and gravitational force? Or is there something else.

 

[haruspex]

Um tension and gravitational force? Or is there something else.

The washer is holding one end of the rope. Where is the other end?

 

[hawkeye1029]

Attached to the washer+bucket side I think.

(Also sorry if I'm being really slow and frustrating, I haven't learned much physics yet)

 

[haruspex]

Attached to the washer+bucket side I think.

right. So what force does that exert on the washer+bucket system?

 

[hawkeye1029]

...tension...? not so sure

 

[haruspex]

...tension...? not so sure

Is the tension the same all along the rope?

 

[hawkeye1029]

I think it's the same correct me if I'm wrong

 

[haruspex]

I think it's the same correct me if I'm wrong

Yes, it's the same. If the tension is T, what is the total of the upward forces on washer+bucket?