Question

Question #c9625

Answer 1

618lbforce

Explanation:

The size of the pool is unimportant, as long as it can hold the cube. Only the depth matters, because this determines the pressure (=force per unit area).

It's a pity this problem was stated in old english measures.
I'll convert to metrical units, and convert the answer back.

`1ft=0,305 m`
`1ft^2=0.305^2=0.0930m^2`

The pressure goes up by `~~10kN//m^2` for every meter down.
(`N`=Newton is the metrical measure for force)

Top of the cube
Is at `9*0.305m=2.745m`
this gives a pressure of `27.450 kN//m^2`
Multiply by area: `F=p*A=27.450*0.093=2.554kN`

The sides
Since pressure rises linearly with depth, we may use the average pressure which will occur halfway up the cube.
Depth halfway is `9.5*0.305m=2.8975m`
Pressure will be `28.975kN//m^2`
Multiply by area: `28.975*4*0.093=10.782kN`

Answer
`F=2.554+10.782=13.336kN~~13.3kN`

Conversion:
`13.3kN=618lb`force.