Work done and Kinetic/Potential Energy

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Hi!

My Physics Class 11 question says that a climber who is 65kg climbs 600m. What is the work done by the climber?

I thought I would have to add both the change in KE and PE. But the answer says that you should simply use mgh (PE).

This is confusing because there should be some work done through movement. Why is KE omitted from calculating the work done that in this case?

Leo asked

Answer:

man climbing a treeMany problems in Physics are solved by making certain approximations and assumptions to avoid complications. If we consider all factors contributing towards the expenditure of energy there may still different factors, but of less importance for the problem under consideration.

In the question we assume that there is no change in Kinetic Energy involved. Work is not to be done to maintain the KE but to change the KE. Though there may be some changes in speed during the process, we disregard the changes and concentrate only on the change in potential energy, which is actually the work done against gravity.

Even if there is a change in Kinetic Energy, then also the work done against gravity will only be the change in potential energy (mgh). He may be doing work against friction and also the change his speed during the climbing process, but the work done against gravity would remain the same (mgh)

If the question had mentioned this (work done against gravitation) then confusion could have been avoided.

 

Hope that the idea is clear now. If you need further clarifications please respond via the comment form.

OPTICS – Question Bank based on Board Question Papers

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Download the following question bank on optics based on CBSE board question papers

Download (PDF, 516KB)

Heat Transfer

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A patient lying in bed is completely covered by a 10mm thick blanket. Above the blanket the air is still and the convective heat transfer coefficient in still air is approximately 3 Wm^-2K^-1. The patient’s skin temperature is stable at 36 degrees Celsius and the air in the hospital is 24 degrees Celsius. What is the rate at which the patient loses heat due to convection and conduction over 1 square metre (in W)?
[The thermal conductivity of the blanket is 0.03 Wm^-1K-1

 

Asked Anurag Ganugapati

Air Pressure – An experiment with syringe

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If I take a medical syringe, position the plunger in the middle of the length of the tube and seal off the tip, I will encounter substantial resistance when I try to move the plunger.
But, if I take the syringe into outer space – no atmosphere – and do the SAME procedure will I notice NO resistance when moving the plunger?  Since there is no air to compress or decompress I suspect there will be no resistance.  Is this correct?

Asked George Creegan

Answer

Yes, the only thing keeping you from pulling the plunger on a syringe with a sealed end is the surrounding air pressure.    If there is perfect vacuum inside and outside the syringe!

 

What is Hall effect ?

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The question was posted by Subhdeep Sarkar.

 

Hall Effect

The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current. It was discovered by Edwin Hall in 1879

Refer to the following links for more information

  1. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/Hall.html
  2. http://farside.ph.utexas.edu/teaching/302l/lectures/node74.html
  3. https://www.youtube.com/watch?v=_ATDraCQtpQ
  4. https://www.youtube.com/watch?v=wpAA3qeOYiI

Sharing an interesting mail received – Mind and Physics

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I meditate regularly. Stay with me, it gets interesting.
Recently I had an experience I need help understanding.
Briefly.
I created, in my imagination, a tree representing my spiritual body.
My roots(below my feet) descend into the Earth.
My trunk is my physical body.
My branches extend into the cosmos.
That’s the image I started with and have been practicing/refining for about a year now.
Recently:
I started “*hearing,” if you can call it that, instructions on how to use the tree metaphor I created.
I heard, “Use your branches to tune-in (like a radio antenna) Gamma frequency waves.”
I heard, “Use your roots to tune-in Theta frequency waves.”
I heard, “Send both to the center of your heart”
(removing some energetic mechanics for brevity)
I heard, “Point them at each other using ^^ energy mechanics, in the center of your heart.”

This may sound out of the Physics arena and firmly in the Meta-Physical arena, I understand, please continue.

My question is thus;
Can Gamma waves interact with Theta waves creating an offset or diffusion of frequency wave patterns resulting in a 3rd Frequency wave pattern?

I was shown/told/insta-learned that this creates an Omega wave displacement field where more metaphysical stuff can then occur within.

*I don’t really “hear” anything. I use that term because it is easier to convey meaning. It is actually more like a hologram of dense information packets that I have called insta-learn. I instantly know things and can manipulate the “image” to “see” the information transference in more detail, just like a 2D hologram plays out its parallax as you move it side to side.

Briefly:
My limited experience using this method is that after I create the displacement field I can breathe into this new non-local space, I can feel it as well. It feels a lot like when you quickly drop on a roller coaster, weightless, for the lack of a better word.

Thank you so much for reading.
If this is not your bag please consider passing it along to someone who fancies themselves a Neuro-naut AND Physicist.

All The Best,

 

Posted by Gerald

Friction – Numerical

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Standing on an icy surface ,a man of mass 60 kg  throws a stone of mass 3 kg horizontally at a velocity of 8 m/s  . How far does he slide back? Coeff of friction -0.02

Asked  Mirja Jakir Hossain

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  • Post Edited: Work done and Kinetic/Potential Energy https://t.co/53bHeenlkr
    about 2 days ago
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