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Homework Help: Equilibrium applications of newton's law of motion

  1. Oct 12, 2009 #1
    A supertanker with the mass of 1.72 *10^8 kg is moving with a constant velocity. Its engines generate a forward thrust of 5.52*10^4 N. Determine (a) the magnitude of the resistive force exerted on the tanker by the water and (b) the magnitude of the upward buoyant force exerted on the tanker by the water.

    I honestly dont know how to do this at all but from the given infor. I thought I could find the sum of forces by M *A but then since it's constant velocity, A would be zero making sume of forces 0. Since it is constant velocity I thought i could use the constant velocity formulas but wasnt sure which one to use since I'm only give mass. I dont even know what kind of force a forward thrust would be considered as.... I am so lost please help!!
  2. jcsd
  3. Oct 12, 2009 #2


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    If you are lost then let's take it in steps.

    The engine produces a thrust (force) of 5.52*104 N (FE)

    Let's call the resistive force Ff.

    So we know the resultant of these two is ma. Now we have an equation ma=FE-Ff.

    But we are told the velocity is constant, which tells you that a=0. So can you get the resistive force now?
  4. Oct 12, 2009 #3
    THANK YOU!!! so I solved it 0=5.52 *10^4-x
    then for part b. The bouyance force is the force that goes up...would be considered same as normal force? and the answer is the same as the mass * g??
  5. Oct 12, 2009 #4


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    I believe that is how it should be done. Although upthrust=weight of fluid displaced = mg =ρVg.

    But they didn't give you V=volume of water displaced. So U=mg will work.
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