Homework Help Forum: Physics Fluids

Posted by Physics Fluids on Friday, October 23, 2009 at 5:20pm.

When a crown of mass 14.7 kg is submerged in water, an accurate scale reads only 13.4 kg. Is the crown made of real gold? Ok How do I do this problem I set up my free body diagram Net Force = ma = 0= Ft + Fb - Fg were Ft is the force of tension on the scale that was used to measure it's apparent weight - Ft = Fb - Fg Ft = Fg - Fb Ft = (mass of object)g - (density of fluid)g(volume of fluid) density of object = (mass of object)/(volume of object) mass of object = (density of object)(volume of object) plug chug Ft = (density of object) (volume of object)g - (density of fluid)g(volume of fluid) ok were do I go from here I think that the volumes are suppose to be the same but I do not see how.

• Physics Fluids - bobpursley, Friday, October 23, 2009 at 5:58pm

  IF the thing is submerged, then volume=mass/densitymaterial The bouyant force is volumedisplaced*denstitywater. bouyantforce= 14.7/densitymaterial*density water. according to the measurements, the bouyant force is 14.7-13.3=1.4g then calculate the density of material: density material= 14.7/1.4 * 1g/cm^3 which is about 10.5g/cm^3 So is this Gold?

  
  

• QUESTION - QUESTION, Friday, October 23, 2009 at 6:15pm

  why are the volumes the same

  
  

• Physics Fluids - QUESTION, Friday, October 23, 2009 at 6:20pm

  Fg on object = (it's density)(it's volume)g Fb = (density of water)(volume of water underneath object pushing it up)gravity your suppose to divide the two gravity is suppose to cancel out and the volume but the volumes are two different objects why are they the same

  
  

• Physics Fluids - bobpursley, Friday, October 23, 2009 at 6:25pm

  What objects do you know when submerged change volume? Certainly chunks of metal do not.

  
  

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