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Homework Help: HELP! Block up incline

  1. Oct 17, 2004 #1
    There's a block of mass M that's pulled up an incline by a force T. The block starts from rest and is pulled a distance L by the force T. The incline, which is frictionless, makes an angle (a) with respect to the horizontal.

    1) Write down the work done by force T.

    That would just be W = T*L right?
    ...Even though net work would be W = TL - mg sin (a)

    2) Calculate the potential energy of the block as a function of the position L.

    U = mgh = mgLsin(a), right?

    3) From the work and the potential energy calculate the kinetic energy of the block as a function of position L.

    Okay... so since the force is conserved, KE + PE + W = 0, right??
    So KE = -W - PE
    = - (TL - mg sin (a)) - mgLsin(a))

    Is that correct or no??

    4) Calculate the acceleration of the block, a, as a function of position L. Calculate the velocity from the acceleration and kinetic energy as a function of position. Show that the kinetic energies calculated in these two ways are equivalent.

    I can't get this part to work. I put acceleration = F/M = (T-mg sin (a)) / m but how do I get it in terms of L? And how do I integrate the acceleration function with respect to L??

    Thank you! All help is greatly appreciated!!
  2. jcsd
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