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Homework Help: Work energy

  1. Oct 11, 2014 #1
    1. The problem statement, all variables and given/known data
    A 310-kg feraligatr slides 3.0m down a 30∘incline at Rainbow Valley and is kept from accelerating by his trainer who is pushing on the feraligatr's back parallel to the incline.

    Express all your answers using two significant figures.
    a Howw much force does the trainer exert?

    How much work does the trainer do on her feraligatr?

    What is the work done by the force of gravity?

    What is the net work done on the feraligatr if friction is ignored?

    Express your answer using two significant figures.

    2. Relevant equations
    W = fd

    3. The attempt at a solution
    well i did net force for the first part which resulted me in to drawing a fbd and I got Applied force which is the trainer minus feraligator which becomes applied force - mgsin30 which got me 1500N which i initially got wrong because of the calculator
    second part i did
    1500*d which is 4600 N (f=fd)
    which then got me confused on part c which i dont understand what does it mean force of gravity
    i dont know how net work works and friction wasnt given in the first place
  2. jcsd
  3. Oct 11, 2014 #2


    User Avatar

    Staff: Mentor

    The animal has dropped by 3.sin 30° metres so it has lost some gravitational P.E. But its speed has not changed, so it has neither lost nor gained K.E. So the P.E. it lost has reappeared as work done somewhere, and we see this has been in opposing the push of the trainer as it moved along the slide. So the work done by gravity is equal to the weight of the animal x the vertical distance gravity pulled it.

    We neglect friction here.
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