I dont understand why this is wrong. can someone me?

  • Thread starter princessfrost
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In summary, mountaineers use a rope to rappel down cliffs. An 82.5 kg climber, 1.54 m tall and with a center of gravity 1.3 m from his feet, rappels down a vertical cliff with his body raised 28.9 degrees above the horizontal. To find the tension needed for the rope, the formula -mg(1.3)sin(28.9) + T(1.3)sin(180-24.2-28.9) = 0 is used. After plugging in the numbers correctly, the tension is found to be 488.61 N.
  • #1
princessfrost
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Mountaineers often use a rope to lower themselves down the face of a cliff (this is called rappelling). They do this with their body nearly horizontal and their feet pushing against the cliff. Suppose that an 82.5 kg climber, who is 1.54 m tall and has a center of gravity 1.3 m from his feet, rappels down a vertical cliff with his body raised 28.9 degree above the horizontal. He holds the rope 1.46 m from his feet, and it makes a 24.2 degree angle with the cliff face.
http://session.masteringphysics.com/problemAsset/1039093/3/YF-11-33.jpg

a) What tension does his rope need to support?




I found the tension to be equal to - mg(1.3) sin(28.9) + T(1.3) sin(180 - 24.2-28.9)=0 and then i solve for T. T= (mg(1.3)sin(28.9))/(1.3sin(180-24.2-28.9)). I plugged in the numbers and found the answer to be 488.61 N but it's wrong. Can someone please help me? Thank you!
 
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  • #2
princessfrost said:
I found the tension to be equal to - mg(1.3) sin(28.9) + T(1.3) sin(180 - 24.2-28.9)=0 and then i solve for T.
You are using the wrong angles. When using [itex]\tau = rF\sin\theta[/itex], the angle is the angle between the position vector (r) and the force.
 
  • #3
ok i got it. thank you sooo much for your help! i really appreciated it!

:)
 

Related to I dont understand why this is wrong. can someone me?

1. Why is it important to understand why something is wrong?

Understanding why something is wrong is important because it allows you to learn from your mistakes and make improvements. It also helps you to identify patterns and potential issues in your work.

2. How can I figure out why something is wrong?

To figure out why something is wrong, you can try to analyze your work and identify any errors or inconsistencies. You can also seek feedback from others or do research on the topic.

3. Is it necessary to know the reason why something is wrong?

While it may not always be necessary, knowing why something is wrong can help you to improve your understanding and skills. It can also prevent similar mistakes in the future.

4. What are some common reasons for something to be wrong?

Some common reasons for something to be wrong include incorrect data, faulty assumptions, and errors in calculations or procedures. It could also be due to a lack of understanding or knowledge on the topic.

5. How can I prevent making the same mistake in the future?

To prevent making the same mistake in the future, you can take note of the reasons why it went wrong and make necessary changes. You can also seek guidance or additional training to improve your skills and understanding.

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