# I Fluid Mechanics: Wooden plank floating in water at an angle

#### TkoT

Summary
it is a worked example. I am confused why the mass of water displaced =(2lp/cos theta),but not (pl/cos theta)?
i think the volume of the water displaced is equal to that of the immersed part OC which is (l/costheta)Xcross-section area. then the mass of water should be pl/costheta, but the answer is not that one. what is the fault in my thinking?

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#### BvU

Homework Helper
Plank has density $\rho = 0.5$. Water has $2\rho$.

I find it much better to use a subscript in such cases: $\rho_{\text {water}}l/\cos\theta$ (plus add an upper limit for $\theta$ for a check later on... )

#### TkoT

Plank has density $\rho = 0.5$. Water has $2\rho$.

I find it much better to use a subscript in such cases: $\rho_{\text {water}}l/\cos\theta$ (plus add an upper limit for $\theta$ for a check later on... )