How much (approx.) does a human arm weigh? Imagine a human man of average size and build, in decent shape, with some degree of muscle tone/definition in the arms (but not action-movie-star bulging biceps). If this man were to lose an arm, about how much would his body weight decrease?
Also, if he gets a prosthetic arm -- absolutely state-of-the-art, most high-tech prosthetic available today -- how much would that weigh? What material would it be made out of?