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Homework Help: Tension in lifting cable

  1. Jul 1, 2007 #1
    1. The problem statement, all variables and given/known data

    A seagoing crane lifts a sealed safe from a sunken ship. The average density of the safe is 5.3 grams/cc and its mass is 120 kg. What is the tension in the lifting cable when the safe is still submerged?

    2. Relevant equations

    Pressure = density *gravity* height*
    Buoyant force = mg

    3. The attempt at a solution

    I calculated 5300kg/m^2 * 9.81 m/s^2 * 120 kg

    The above is what I got so far but I'm not sure I'm doing it right. Any help would be greatly appreciated.
  2. jcsd
  3. Jul 1, 2007 #2
    Draw a free-body diagram of the object. From the context of the problem, there must be no net force acting on the object. What forces act in which directions?

    Note: the buoyant force is equal to the weight of the DISPLACED fluid, not necessarily equal to the weight of the submerged object.
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