Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

Let, diameter of cylinder hole of height 30m and diameter 2m filled with water. In a book, when author tried to find out the power for lifting all of the water then he used average height. why is that. I mean he wrote average height $ h = \frac{0+30}{2}$. why is that?

share|improve this question
3  
I don't know how to answer without more details from the problem. He might be treating the water as a single object. Then the work done in lifting it out of the container will be equal to the work done in lifting a single particle with mass equal to the water, concentrated at the water's center of mass. The water's center of mass is initially at $y=15$ m. –  elfmotat Feb 23 '13 at 9:10
    
@elfmotat: Sounds good to me. You should make a real answer out of that. –  Rafael Reiter Feb 23 '13 at 9:14
1  
But what is the problem, If I do not consider as a single object, so i will use the formua $p= \frac{mgh}{t}$ but they are using $p= \frac{mgh}{2t}$ because of center of mass. –  ghost Feb 23 '13 at 11:56
add comment

Know someone who can answer? Share a link to this question via email, Google+, Twitter, or Facebook.

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.