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What is the force exerted by a boulder on the bottom of a tank filled with water?

  1. Oct 9, 2012 #1
    I know the weight of the boulder is 20,000 N and the volume is 0.4 m^3
    Wouldn't the answer just be 20,000? Since the force is the same thing as weight?
    the options are:

    (a) 12,460
    (b) 17,860
    (c) 16,080
    (d) 14,450
    (e) none of these
     
  2. jcsd
  3. Oct 9, 2012 #2
    I think this is what your looking for...

    pressure = force/ area

    p = 20000/0.4
    = 50000 N/m^2
     
  4. Oct 9, 2012 #3

    NascentOxygen

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    Staff: Mentor

    Weight is a force of attraction due to gravity, yes.
    Do you know a value for the density of water?
     
  5. Oct 9, 2012 #4

    Doc Al

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    Staff: Mentor

    No. What effect does surrounding the boulder with water have?
     
  6. Oct 9, 2012 #5
    Oohhh, so I would calculate the buoyant force and then subtract that from the weight of the boulder, so I get the force that the boulder exerts on the ground?

    If I multiply volume x density of water x force of gravity:
    0.4 x 1000 x 9.8 = 3920
    and then subtract this from 20,000 I get 16080.
    Is that right?
     
  7. Oct 9, 2012 #6

    Doc Al

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    Staff: Mentor

    Exactly.

    Looks good to me.
     
  8. Oct 9, 2012 #7
    Thank you!!!! :)
     
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