# Homework Help: Static hydraulics, calculate water depth

1. Dec 3, 2011

### escobar147

1. The problem statement, all variables and given/known data
Refer to Figure 3. A steel box (250 mm x 250 mm x 250 mm) is placed at the bottom of a tank. If the pressure on the top surface is 10000 Pa, what is the water depth in the tank?

a. 1019 mm
b. 251.02 mm
c. 1269 mm

water density: 1000 kg/m3
gravity: 9.81

2. Relevant equations
P=pgh

3. The attempt at a solution

if the pressure on the top surface f the box is 10,000pa, then by rearranging the formulae P=pgh you get:

10,000= 1000 x 9.81 x h

solving for h:

h = 0.981 meters

adding the depth at the top of the box to the height of the box to find the final depth of the tank=

981mm + 250mm = 1231mm

however this is not the correct answer?

2. Dec 3, 2011

### nvn

escobar147: You simply made an obvious algebra mistake. Try again. Also, always leave a space between a numeric value and its following unit symbol. E.g., 250 mm, not 250mm. Also, the unit symbol for pascal is Pa, not pa. Lowercase p means pico. It should be 10 000 Pa.

3. Dec 4, 2011

### escobar147

omg i have just realized my mistake. i incorrectly re-arranged the formula, the actual answer is this:

P = pgh

10,000 = 1000 x 9.81 x h

10,000 = 9810 x h

10,000/9810 = 1.01936 meters

1.01936 meters + 250 mm

= 1.269 meters.

thanks for your help nvn i appreciate it!