Calculate the resultant thrust and overturning moment

[Taidhg]

Homework Statement

A vertical retaining gate 2metres X 24metres hinged about the bottom edge of a dry dock has water to a depth of 21 metres on one side. Calculate the Retaining Force at the middle of the free upper edge of the gate to keep it shut in the vertical position. With the density of seawater being 1030Kg/m³.

Homework Equations

Hydrostatic pressure = D*g*h
Force = P*A
Thrust force = D*g*(h/2)*A
Overturning moment = Thrustforce*(h/3)

The Attempt at a Solution

I am sorry I really don't understand this question.

 

[Spinnor]

Is this a picture of the problem? It seems to me that the weight and density of the gate is needed?

 

[Taidhg]

View attachment 235477

Is this a picture of the problem?

I wasn't provided with a diagram however that is the same as the one I produced

 

[Spinnor]

I wasn't provided with a diagram however that is the same as the one I produced

I thought the thickness of the gate was 2m. The height I guess is 2 meters, the width is 24, and the gates thickness is small. You need to integrate the total torque on the gate and equate that with 2xF ?

I would be wrong. The height must be 24m and the width 2m which makes for a very tall and narrow gate. Now I'm confused also.

 

[gneill]

The gate is 2 meters in width, 24 meters high, and its thickness is irrelevant. Think about how you might calculate the torque about the hinge's axis due to the water pressure.

 

[Spinnor]

and its thickness is irrelevant

If it is thick then its weight might contribute a torque. But that info was not given.

 

[gneill]

If it is thick then its weight might contribute a torque. But that info was not given.

Place the hinge in the center of the door thickness. Problem solved