Mark asked in Science & MathematicsPhysics · 1 month ago

Lost Energy Question?

Where does lost energy go in a Atwood Machine

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2 Answers

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  • Anonymous
    1 month ago

    Almost all of it to friction in the pulley.

  • oubaas
    Lv 7
    1 month ago

    No lost energy at all : the change on initial GPE becomes KE on hanging masses !!!

    I guess that an exemple will  convince you more than lots of words ; lets' assume :

    m1 = 4 kg @ ho = 10 m 

    m2 = 2 kg @ ho' = 0 m (on the ground)

    g = 10 m/sec^2 

    initial gravit. potential energy GPEo = 10(4*10+2*0) = 400 joule 

    acceleration a = g(m1-m2)/(m1+m2) = 10*2/6 = 10/3 of m/sec^2

    after 1.5 sec of motion :

    speed V = a*t = 10*1.5/3 = 5 m/sec

    kinetic energy KE = (4+2)/2*5^2 = 3*25 = 75 joule 

    height change Δh = V*t/2 = 2.5*1.5 = 3.75 m  

    final gravit. potential energy GPE = (10-3.75)*10*4+(3.75*10*2) = 325 joule 

    GPE+KE = 325+75 = 400 joule = GPEo  ...Q.E.D. 

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