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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.

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