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Doubt: Basic question on Work-Energy Method?

  1. Sep 5, 2013 #1
    I have a basic doubt on application of work energy method,

    1. Can I apply work-energy method (i.e. work done equals to change in kinetic energy(KE)) for a body sliding down the inclined plane? If yes, while solving the problem i should use only change in KE or sum of change in KE & PE(potential energy), as heigh of the body is changing while sliding down? I am pretty confused kindly explain in detail..

    2. What if in case of a a body vertically moving down/falling? In this case, it should be KE only or PE only or Sum of KE&PE? and Why?

    I referred some books and while solving any of the above problems, they used work done = change in kinetic energy, i am confused why they are not considering PE in these situations?

    Kindly reply ASAP, need a clear explanation....Many thanks in advance...
  2. jcsd
  3. Sep 5, 2013 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Yes you can apply it. See my comment below.

    Again, see my comment below.

    The work-energy theorem says that if you consider the work done by all forces (including gravity) it will equal the change in the kinetic energy (not total energy). And that's just what happens.

    If you consider the work done by all forces except gravity, then the work done will equal ΔK + ΔU. (The work done by gravity is already included in the potential energy term.)
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