Question #c9625

1 Answer
MeneerNask ยท dwayne
Jan 31, 2015

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=618lbforce.

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