physics: mass,density and volume

• iforgottenx

  25 Jan 12, 18:38

  hey~ i need help in physics . 

  Q1~ Iron has density of 7900kg/m^3 . what is the volume of 2000g of iron? 

   

  Q2 Given that the density of air is 1.25kg/m^3,what is the mass of air in a room of size 6m by 5m by 3m?

• ThunderFbolt

  25 Jan 12, 18:50

  What is the definition of density?
  
  Also... By just looking at the units (kg / m^3 and g), how would you find the volume (which is in m^3)? Same for question 2. This is usually a good hint when you don't know your work. 

• iforgottenx

  25 Jan 12, 19:10

  i done it but it seems wrong, anyone enlighten me pls, my working below:

  Q1  7900kg/m^3 x 2kg = 15800m^3

  Q2 1.25kg/m^3 = mass/90m^3 

         Mass=1.25kg/m^3 x 90m^3=112.5kg 

  Got any error or if its correct tell me pls 

• ThunderFbolt

  26 Jan 12, 01:34

  Let's take it back to basics. What is the definition of density? What is the formula?

• ascklee

  26 Jan 12, 16:53

  Whoa ... reasonableness suggests that 15800m^3 cannot be correct.  15800m^3 of iron is a lot of iron -- roughly 25 m by 25 m by 25 m of it.  The answer is (2/7900) m^3 of iron.  The answer to Q2 is correct.

   

  Sincerely,
  CKLee
  Founder,
  OpenlySolved.org

• Darkness_hacker99

  26 Jan 12, 17:25

  Physics...  

  Density is mean the amount of particular in a volume.

  Densite of iron you've given 7900kg/m^3. If you were to visualize it (I always tell my student), it would mean a block of iron metal 1m x 1m x 1m, weighs 7900kg.

  Now with this image of the iron block, I wanna you scale down the block of iron till it weighs 2kg. The 2kg iron block would definitely has lesser volume than 1m^3