# A difficult problem with dynamics

• doodijh
In summary, the problem presents a scenario in which Tarzan, who weighs 100kg, holds one end of a flexible and strong vine while Jane, who weighs 50kg, hangs on the other end above a river filled with crocodiles. A sudden storm has removed all friction, and the question asks for the acceleration of Tarzan towards the edge of a cliff. Although Tarzan is the only one moving, Jane's weight plays a significant role in the acceleration as it provides the force that moves both of them.
doodijh
This is problem from the extension section from my Gr.12 physics textbook

## Homework Statement

Tarzan (m=100kg) hold one end of an ideal vine (infinitely strong, completely flexible, but having zero mass) The vine runs horizontally to the edge of a cliff, then vertically where Jane (m=50kg) is hanging on,above a river filled with crocodiles. A sudden sleet storm has removed all friction. Assuming that Tarzan hangs on, what is the acceleration toward the cliff edge?

## Homework Equations

Newton's laws of motion.
Projectile motion.

## The Attempt at a Solution

Horizontal & vertical distance is not given, making it absolutely difficult to apply projectile applications.
I know that for Tarzan
(horizontally) Fnet = Tcosθ
(vertically) Fnet = Tsinθ - Fg b/c he will be moving on the vine.
I know that for Jane,
0=T-Fg, since she is in a stable position
T=Fg
I am completely lost on this question, can anybody help me or hint to me something about the solution.

doodijh said:
This is problem from the extension section from my Gr.12 physics textbook

## Homework Statement

Tarzan (m=100kg) hold one end of an ideal vine (infinitely strong, completely flexible, but having zero mass) The vine runs horizontally to the edge of a cliff, then vertically where Jane (m=50kg) is hanging on,above a river filled with crocodiles. A sudden sleet storm has removed all friction. Assuming that Tarzan hangs on, what is the acceleration toward the cliff edge?

## Homework Equations

Newton's laws of motion.
Projectile motion.

## The Attempt at a Solution

Horizontal & vertical distance is not given, making it absolutely difficult to apply projectile applications.
I know that for Tarzan
(horizontally) Fnet = Tcosθ
(vertically) Fnet = Tsinθ - Fg b/c he will be moving on the vine.
I know that for Jane,
0=T-Fg, since she is in a stable position
T=Fg
I am completely lost on this question, can anybody help me or hint to me something about the solution.

Jane's weight provides the force that accelerates the combined mass of both Tarzan and Jane. Draw free body diagrams for both T and J -- that should help.

Where the heck is Cheeta anyway?

berkeman said:
Jane's weight provides the force that accelerates the combined mass of both Tarzan and Jane. Draw free body diagrams for both T and J -- that should help.

Where the heck is Cheeta anyway?

Who is Cheeta?
look at the attached file to see the diagram .. Tarzan is accelerating toward Jane ..

#### Attachments

• Tarzan.jpg
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Here is the free body diagram .. yet it can not be used to find the acceleration if tension is not given

#### Attachments

• freebody.jpg
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doodijh said:
Who is Cheeta?
look at the attached file to see the diagram .. Tarzan is accelerating toward Jane ..

LMAO. Obviously you haven't done your background research on Tarzan:

http://en.wikipedia.org/wiki/Tarzan

Cheeta is the chimp who should be trying to save T & J. Jeeze.

And back on-topic, Tarzan's weight (the mg vector down in the FBD) doesn't matter, since he is on a frictionless surface. All he does is add to the mass that Jane's weight accelerates. The tension in the vine pulls T horizontally to accelerate him. J's weight is what causes the force that accelerates them both as a coupled system.

Show us a combined drawing of them both, showing the tension force in the vine, J's weight vector, and the accelerating force on T. Use the equation for the sum of F = ma.

berkeman said:
LMAO. Obviously you haven't done your background research on Tarzan:

http://en.wikipedia.org/wiki/Tarzan

Cheeta is the chimp who should be trying to save T & J. Jeeze.

And back on-topic, Tarzan's weight (the mg vector down in the FBD) doesn't matter, since he is on a frictionless surface. All he does is add to the mass that Jane's weight accelerates. The tension in the vine pulls T horizontally to accelerate him. J's weight is what causes the force that accelerates them both as a coupled system.

Show us a combined drawing of them both, showing the tension force in the vine, J's weight vector, and the accelerating force on T. Use the equation for the sum of F = ma.

LOL .. now I'm fine with Cheeta .. but your explanation still doesn't make sense.
Why?
the question is asking for the acceleration toward the edge of a cliff, and the only person moving is Tarzan, and not Jane. Therefore, the question asks for the acceleration of Tarzan, and so there is no such thing as coupled system as what you've said. Jane's weight has nothing to do with Tarzan's acceleration too b/c again, the question is asking Tarzan acceleration as he reaches Jane.
Note: the cliff edge is behind the river, and Jane is on the river. Look at the attached file. Remember what the question says "The vine runs horizontally to the edge of a cliff, then vertically where Jane (m=50kg) is hanging on,above a river filled with crocodiles"

ok.

#### Attachments

• tarzan pic.jpg
19 KB · Views: 568
doodijh said:
LOL .. now I'm fine with Cheeta .. but your explanation still doesn't make sense.
Why?
the question is asking for the acceleration toward the edge of a cliff, and the only person moving is Tarzan, and not Jane. Therefore, the question asks for the acceleration of Tarzan, and so there is no such thing as coupled system as what you've said. Jane's weight has nothing to do with Tarzan's acceleration too b/c again, the question is asking Tarzan acceleration as he reaches Jane.
Note: the cliff edge is behind the river, and Jane is on the river. Look at the attached file. Remember what the question says "The vine runs horizontally to the edge of a cliff, then vertically where Jane (m=50kg) is hanging on,above a river filled with crocodiles"

ok.

Of course Jane's weight is the driving force in the acceleration of both J & T. The vine pulls T horizontally because J's weight is pulling down on the vine. Not sure where the disconnect is here... Unless I'm misreading it, this is a pretty standard question in intro physics.

Shouldn't the overall diagram look like this?

berkeman said:
Of course Jane's weight is the driving force in the acceleration of both J & T. The vine pulls T horizontally because J's weight is pulling down on the vine. Not sure where the disconnect is here... Unless I'm misreading it, this is a pretty standard question in intro physics.

First, the vine does not act as a pully -> go back to what the question says. Jane is in a separate vine, in a stable position.

For Diazona, I do not think your diagram is correct b/c vine by definition is a weak-stemmed plant that derives its support from climbing. Look back at the question >> A sudden sleet storm has removed all friction. Friction stands for air resistence.

It is important to read the question carefully before you answer it >> that goes for both of you.

There is no solution for this problem at the back of the text, however if its diagram is as easy as Diazona's, then it can be solved easily.

doodijh said:
First, the vine does not act as a pully -> go back to what the question says. Jane is in a separate vine, in a stable position.
No where does it mention that Jane is on a second vine. Only one vine is mentioned.

For Diazona, I do not think your diagram is correct b/c vine by definition is a weak-stemmed plant that derives its support from climbing. Look back at the question >> A sudden sleet storm has removed all friction. Friction stands for air resistence.
Diazona's diagram seems like a reasonable interpretation of this ambiguously presented problem. Why do you think friction stands for air resistance? Wouldn't you think that a sleet storm would coat the surface with ice, thus removing any friction that Tarzan could use to prevent his sliding towards the edge?

It is important to read the question carefully before you answer it >> that goes for both of you.

There is no solution for this problem at the back of the text, however if its diagram is as easy as Diazona's, then it can be solved easily.
That's what I would do.

doodijh said:
It is important to read the question carefully before you answer it >> that goes for both of you.
It goes for you too, you know... specifically concerning this part:
doodijh said:
The vine runs horizontally to the edge of a cliff, then vertically

(Generally speaking, it's also important not to dismiss out of hand the ideas offered by the people who are trying to help you. But I'm not complaining )

## 1. What is meant by "difficult problem with dynamics" in science?

"Difficult problem with dynamics" in science refers to a complex and challenging issue related to the study of motion and forces in a system. It may involve complicated mathematical calculations or require advanced understanding of principles such as Newton's laws of motion.

## 2. What are some common examples of difficult problems with dynamics?

Some common examples of difficult problems with dynamics include analyzing the motion of celestial bodies, predicting the behavior of complex fluid dynamics, or understanding the mechanics of a moving object in a high-pressure environment.

## 3. What makes solving these problems challenging for scientists?

Solving difficult problems with dynamics can be challenging for scientists due to the need for precise measurements, the complexity of the systems involved, and the need to consider multiple variables and forces at play. Additionally, these problems often require advanced mathematical skills and techniques.

## 4. How do scientists approach solving difficult problems with dynamics?

Scientists approach solving difficult problems with dynamics by using a combination of theoretical models, experimental data, and computational methods. They may also collaborate with other scientists and utilize advanced technology and equipment to aid in their analysis.

## 5. What are the potential real-world applications of studying difficult problems with dynamics?

Studying difficult problems with dynamics has many potential real-world applications, such as improving the design and efficiency of transportation systems, developing more accurate weather forecasting models, and understanding the behavior of complex biological systems. This knowledge can also be applied to various engineering and technological advancements.

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