C10B.11 While holding onto a horizontal bar, you do a pull- up, slowly lifting y

Question

C10B.11 While holding onto a horizontal bar, you do a pull- up, slowly lifting your center of mass a distance h. If we assume you are moving very slowly at each stage of this process, then the bar will exert an upward force on your hands that is essentially equal to your weight throughout C1 the process. (a) Describe the work that various external forces do on you during the process, and argue that the net work (b) This is energy flowing out of you. Where do you think (c) Now define the system to be you and the earth. Where done on you is -mlglh, where m is your mass. this energy might be coming from? does the energy that flows out of you go

Explanation / Answer

Bar is lifting slowly so it has not any kinetic energy. And it has lifted h hight from ground.

(A) from work energh theoram - total work done on rode is equal change in kinetic energy

W(gravity) + w(my) = change in kinetic energy = 0

-mgh + W(my) =0

W(my) =mgh

(B) to do this work required energy in comming from out body. That is stored in our body

(C) in this process work is done against gravitational field so this energy is stored as a potential energy of bat in gravitational field

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