John is carrying a shovelful of snow. The center of mass of the 3.00 kg of snow he is holding is 15.0 cm from the end of the shovel. He is pushing down on the opposite end of the shovel with one hand and holding it up 30.0 cm from that end with his other hand. Ignore the mass of the shovel. Sarah says that his hand pushing down on the shovel must be exerting a greater force than the hand pushing up. James says it is just the reverse. Which one, if either, is correct?
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Sarah, because the hand pushing down must exert a greater force to match the torque exerted by the snow.
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James, because, depending on the location of the axis of rotation, the hand pushing down can counteract the torque exerted by the snow.
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James, because the hand pushing up must exert a force that equals the sum of the force of the hand pushing down and the weight of the snow.
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James, because both (b) and (c) above are correct.
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Neither, because the hands exert forces of equal magnitudes.
Kids playing with snow
Renzo Piano, Jean-Marie Tjibaou Cultural Center, Nouméa, New Caledonia. 1991–98.
John Singer Sargent, The Daughters of Edward Darley Boit.
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A longitudinal cut through the center of a shoot top of Coleus, a eudicot