Question from AAMC regarding specific gravity

[Tennisfam]

I'm taking the AAMC practice exams, and I need someone to help me understand one of the questions and answers. If you could give me a simple explanation rather than complicated, that would be perfect.

The question is, "An object with 15 grams mass is immersed in benzene and suffers an apparent loss of mass 5 grams. What is the approximate specific gravity of the object? (The specific gravity of benzene is 0.7)"

The answer is 2.1.

Thanks!

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[ssj4vinh]

Remember that the displaced volume of the liquid is the same as the volume of the object. Here, the buoyant force (the upward force which causes the 'apparent loss of mass') is 1/3 of the force acting downward due to the object's mass. This means that the liquid (in this case benzene) is 1/3 of the density of the object. 0.7 x 3 = 2.1

The wording "apparent loss of mass 5 grams" might throw some people off, but it just means buoyant force.

 

[Tennisfam]

Thanks!