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Pressure and mass density

  1. Oct 7, 2009 #1
    1. The problem statement, all variables and given/known data
    A spring sticks up from the bottom of the sink, 0.20[m] long ; when a light (ρ=750[kg/m³]) wood block (0.2[m,x]×0.2[m,y]×0.1[m,z]) is attached on top of it, the spring becomes 0.05[m] long.


    2. Relevant equations
    mass density = mass / volume
    Fspring = -ks



    3. The attempt at a solution

    a) weight of block = 3kg
    stiffness of spring???
    b & the others.. ??
     
  2. jcsd
  3. Oct 7, 2009 #2
    What do you need to determine?
     
  4. Oct 7, 2009 #3
    a) calculate the weight of the block, and the spring's stiffness.
    b) Write the Forces applied to the block if the sink is filled until the block's top is .05[m] below water surface (ρ=1000[kg/m³]).
    c) calculate the Pressure Force on block's top and on block's bottom. (Patmosphere=10000[N/m²])
    d) What will the spring's length become, when the block is submerged?
     
  5. Oct 7, 2009 #4
    - for spring stiffness all you need to think about is the formula for the force exerted by a spring. draw your free body diagram. There will only be two forces...

    - what do you think adding water does? the question already gives you a great hint in that it gives you the density of water...
     
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