일반물리학 1 — Fluids: Problem 3

3 In Fig. 14-22, water stands at depth $D = 30.0 \text{ m}$ behind the vertical upstream face of a dam of width $W = 250 \text{ m}$. Find (a) the net horizontal force on the dam from the gauge pressure of the water and (b) the net torque due to that force about a horizontal line through $O$ parallel to the (long) width of the dam. This torque tends to rotate the dam around that line, which would cause the dam to fail. (c) Find the moment arm of the torque.