Question

how tall must a water filled manometer be to measure blood pressure as high as 300 mm Hg? what do i use for pressure, density and height?

Answer 1

It has to be 13.6 times higher than the maximum mercury column height. (13.6 is the mercury/water density ratio.)

Answer 2

Sorry, still confused. I get that the density for mercury is 13.6x10^3 kg/m^3. All I know is that the answer is 4.08m, I just don't know how to get there. Do I use P=density*gravity*height
h=pressure/density*9.8
but my answer didn't even come close to 4m

Answer 3

If you multiply the mercury manometer maximum reading of 0.3 m by 13.6, which is what I suggested, you get the correct answer. 4.08 meters.

For the same value of P, if liquid density is 1/13.6 as high (as it is with water), H must be 13.6 times higher.