When the Tucurui Dam was constructed in northern Brazil, the lake that was created covered a large forest of valuable hardwood trees. It was found that even after 15 years underwater the trees were perfectly preserved and underwater logging was started. During the logging process a tree is selected, trimmed, and anchored with ropes to prevent it from shooting to the surface like a missile when cut. Assume that a typical large tree can be approximated as a truncated cone with a base diameter of 8 ft , a top diameter of 2 ft , and a height of 100 ft . Determine the resultant vertical force that the ropes must resist when the completely submerged tree is cut. The specific gravity of the wood is approximately 0.6.

Respuesta :

Answer:[tex]F_{net}=803.712 lbf[/tex]

Explanation:

Given

[tex]d_1=8 ft[/tex]

[tex]d_2=2 ft[/tex]

height=100 ft

specific gravity=0.6

[tex]Volume of tree=\frac{\pi \cdot h}{3}\left [ r_1^2+r_2^2+r_1r_2\right ][/tex]

[tex]V=\frac{\pi \cdot 100}{3}\left [ 8^2+2^2+8\cdot 2\right ][/tex]

[tex]V=8798.6 ft^3[/tex]

Now net upward force on log

[tex]F_{net}=\rho _{water}Vg-mg[/tex]

[tex]F_{net}=\left ( \rho _{water}-\rho \right )Vg[/tex]

[tex]F_{net}=\left ( 1-0.6 \right )\times 62.4\times 32.2[/tex]

[tex]F_{net}=803.712 lbf[/tex]

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