Change the chapter
Question
(a) What is the density of a woman who floats in freshwater with 4.00% of her volume above the surface? This could be measured by placing her in a tank with marks on the side to measure how much water she displaces when floating and when held under water (briefly). (b) What percent of her volume is above the surface when she floats in seawater?
Question by OpenStax is licensed under CC BY 4.0.
  1. $960 \textrm{ kg/m}^3$
  2. $6.34 \%$
Solution Video

OpenStax College Physics for AP® Courses Solution, Chapter 11, Problem 46 (Problems & Exercises) (1:40)

Sign up to view this solution video!

Rating

No votes have been submitted yet.

Quiz Mode

Why is this button here? Quiz Mode is a chance to try solving the problem first on your own before viewing the solution. One of the following will probably happen:

  1. You get the answer. Congratulations! It feels good! There might still be more to learn, and you might enjoy comparing your problem solving approach to the best practices demonstrated in the solution video.
  2. You don't get the answer. This is OK! In fact it's awesome, despite the difficult feelings you might have about it. When you don't get the answer, your mind is ready for learning. Think about how much you really want the solution! Your mind will gobble it up when it sees it. Attempting the problem is like trying to assemble the pieces of a puzzle. If you don't get the answer, the gaps in the puzzle are questions that are ready and searching to be filled. This is an active process, where your mind is turned on - learning will happen!
If you wish to show the answer immediately without having to click "Reveal Answer", you may . Quiz Mode is disabled by default, but you can check the Enable Quiz Mode checkbox when editing your profile to re-enable it any time you want. College Physics Answers cares a lot about academic integrity. Quiz Mode is encouragement to use the solutions in a way that is most beneficial for your learning.

Calculator Screenshots

OpenStax College Physics, Chapter 11, Problem 46 (PE) calculator screenshot 1
Video Transcript
This is College Physics Answers with Shaun Dychko. A women floating in freshwater has a fraction above the water, 4 percent, which is 0.0400. The fraction above plus the fraction submerged has to equal 1 and so we know what the fraction submerged is, we have a formula for that— that is the density of the women on average divided by the density of the fluid that she's in, which in this case is freshwater. So the fraction submerged is 1 minus the fraction above water so that's 1 minus 0.0400 which is 0.9600 and we also have this expression for the fraction submerged and we can then figure out the average density by multiplying both sides by density of water and so we have the average density of the woman is the fraction submerged times the density of the water. So it's 0.9600 times 1.000 times 10 to the 3 kilograms per cubic meter which is 960 kilograms per cubic meter. Part (b) asks what fraction would be above the water if she was in seawater? Well the fraction above is 1 minus the fraction submerged, if we rearrange this, and so that's 1 minus her density divided by the density of seawater. So that's 1 minus 960 kilograms per cubic meter divided by 1.025 times 10 to the 3 kilograms per cubic meter times a 100 percent and that is 6.34 percent above the water and so that almost is 50 percent more above the water than in freshwater.