fishslayer Posted November 8, 2009 Share Posted November 8, 2009 I got this question sent to me: An 2 kg mass object is held by a spring balance in a liquid of density 1200kg/m3. What reading does the spring balance show (in N)? So i wanted to cheak my that i was doing it properly can somebody cheak what i did and say. This is what i did. Weight = mg Weight = 2*10 Weight = 20 Upthrust = Density of liquid/ Density of Solid (mg) So: Density of solid = Density of liquid (mg) Denity of solid = 1200*20 Density of Solid = 24000 Apparent wieght = mg (1- density of liquid/density of solid) = 20 (1- 1200/24000) = 20 (1- 0.05) = 20*0.95 = 19N Is that right? Link to comment Share on other sites More sharing options...
John Cuthber Posted November 8, 2009 Share Posted November 8, 2009 There isn't enough information to answer the question. Imagine 2 Kg of polystyrene foam hanging from a balance. If you put it in a container of water it would float and aparently weigh nothing. Link to comment Share on other sites More sharing options...
DJBruce Posted November 9, 2009 Share Posted November 9, 2009 You are correct in that: [math]m_{b}=m_{o}\left(1-\frac{p_{f}}{p_{o}}\right)[/math] However your calculation of density is incorrect. According to your calculations your density has the units of [math] \frac{kg^{2}}{m^{2}s^{2}}[/math] which is not right. Unless you have a volume for the immersed solid there is not enough information to do this question. Link to comment Share on other sites More sharing options...
fishslayer Posted November 9, 2009 Author Share Posted November 9, 2009 Ok thank you for your help (i kind have knew i couldnt be right ) Link to comment Share on other sites More sharing options...
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