Hi there, There's a problem in our 8th grade science book that I don't understand how to solve. Of course the teacher's edition gives me the answer, but with no explanation. Just the answer. Since this subject matter is not my strong suit, I need some help. Question: The specific gravity of liquid hydrogen is 0.07. If the pressure at the bottom of a 50 ft high tank of water is 22 psi, what would be the pressure at the bottom of the same tank if it were filled with liquid hydrogen instead? Book's answer: 1.54 psi (0.07 x 22 psi) The only formulas explained in the text just before this question are specific gravity= density of water/density of water and pressure= force/area I don't think either of these formulas apply to this; however, I may be wrong. And if one does apply, please explain how. Thanks for any help! I can't stand telling kids "that's the answer because the book says it is!"

I tried to manipulate the formulas you gave, to obtain the answer. Formulas: density= mass / volume d=m/V pressure=Force/area= (mass*gravity force)/area p=F/A=(mg)/A specific gravity=substance density / water density Let's use these abbreviations: d_H = hidrogen density d_W = water density m_H = hidrogen mass m_W = water mass _______________ We know that p_H= F/A = (m_W*g)/A On the other hand d_W=(m_W*g)/A <=> A=(m_W*g)/22 (since d_W=22) Substituting this on the first equation we get p_h= (m_H*g)/(m_W*g/22) = m_H/m_W * 22 = (m_H*V)/(m_W*V)*22= d_H/d_W * 22 = 0,07 * 22