Q.

A hemispherical portion of radius R is removed from the bottom of a cylinder of radius R. The volume of the remaining cylinder is V and its mass M. It is suspended by a string in a liquid of density ρ where it stays vertical. The upper surface of the cylinder is at a depth h below the liquid surface. The force on the bottom of the cylinder by the liquid is      [2001]

1 Mg  
2 Mg-Vρg  
3 Mg+πR2hρg  
4 ρg(V+πR2h)  

Ans.

(4)

From Archimedes principle

Upthrust=wt. of fluid displaced

Now, Fbottom-Ftop=Vρg

Fbottom=Ftop+Vρg

=P1×A+Vρg

=(hρg)×(πR2)+Vρg

=ρg[πR2h+V]