Fluid pressure question in US units

[freshman2013]

Homework Statement

The ocean liner Titanic lies under 12500 feet of water at the bottom of the Atlantic Ocean. (The density of water is 62.4 lb/ft{}^3.)

What is the water pressure at the Titanic? (Give your answer in both pounds per square foot and pounds per square inch.)

Homework Equations

pressure=ro*g*h

The Attempt at a Solution

at first, all I did was multiply 62.4*32(g in ft/s^2)*12500. The answer was wrong and then I think I found out why. I multiplied the units (lb/ft^3)*(ft/s^2)*ft and got lb/(ft*s^2) instead of lb/ft^2. Anyone get what I'm supposed to do for this problem? I never had this problem when working with metric units since kg/(m*s^2) converts nicely to N/m^2 Thanks!

 

[Chestermiller]

Homework Statement

The ocean liner Titanic lies under 12500 feet of water at the bottom of the Atlantic Ocean. (The density of water is 62.4 lb/ft{}^3.)

What is the water pressure at the Titanic? (Give your answer in both pounds per square foot and pounds per square inch.)

Homework Equations

pressure=ro*g*h

The Attempt at a Solution

at first, all I did was multiply 62.4*32(g in ft/s^2)*12500. The answer was wrong and then I think I found out why. I multiplied the units (lb/ft^3)*(ft/s^2)*ft and got lb/(ft*s^2) instead of lb/ft^2. Anyone get what I'm supposed to do for this problem? I never had this problem when working with metric units since kg/(m*s^2) converts nicely to N/m^2 Thanks!

In the US system, the unit of mass that applies for use in Newton's second law and for getting the gravitational force on a body is the slug. The mass in slugs is equal to the mass in lb_m divided by the average gravitational acceleration at the Earth's surface 32.2. Alternately, some people express Newton's second law in a little different form:

F = ma/g_c

where F is the force in lb_f, m is the mass of the body in lb_m, a is the acceleration in ft/sec² and

$$g_c=32.2 \frac{lb_m}{lb_f}\frac{ft}{sec^2}$$

The difficulty with the english system is the term pounds (lb) is used for both mass (lb_m) and force (lb_f); these are different entities.